From 1850 to the Meiji Restoration
In the early 1850s, Japan was under the reign of the Tokugawa shogunate. This government had been installed in 1603, ending the long period of internal quarreling and war and replacing it with 250 years of peace. The center of this government, the city of Edo, had grown to be the world’s largest city, with over one million inhabitants in the late 18th century.
The Tokugawa shogunate had managed to attain great stature. It had drawn from the Emperor virtually all power, had moved the government from Kyoto to Edo, and had closely bounded each of the provincial rulers of the feudal system to the shogun. One of the primary reasons that this system, which had gone out of fashion in Europe almost a hundred years earlier, could remain working for such an extended period was a careful guarding by the shogunate of the principal values of the Japanese society. It allowed virtually no commercial contact with foreign countries (beyond the Netherlands and China, which were both allowed remote trading posts), and no contact whatsoever between the population and the foreigners, and had banned all voyages abroad.
Thus, it was with considerable shock that it experienced the arrival of an U.S. expedition led by Commodore Matthew Calbraith Perry which arrived in the bay that bordered Edo. The black ships of this fleet, powered by steam and radiating a mysterious grace and imminent power, seeking nothing more than the delivery of a letter to the Emperor asking for commercial relations, and possibly the release of imprisoned American whalersmen that had strayed to close to Japanese waters, brought with them a clearly obvious threat. No longer could Japan isolate itself from the outside. It now had to choose either voluntary abandonment of its most closely guarded principle, or go down under the pressure of imperialist powers, much like its neighbor, China, was doing at the very same time.
And thus, when Perry returned with his fleet from its winter quarters in Macao, he was greeted with an invitation for extended talks on the matter of trade relations. The Treaty of Kanagawa spelled an end to Japan’s isolationism and inner peace. 
Swiftly, opposition against the foreigners erupted. Violence, hatred, open hostilities against the outsiders, led by young samurai who had the support of the powerless Emperor in Kyoto, flared up in the early 1860s. Britain, France, the Netherlands and the U.S. sent warships to bombard the harbors of Kagoshima and Shimonoseki in 1864. In the flames of the bombardment, the revolution turned from the all too powerful outsiders to the Tokugawa shogunate. Provincial leaders marched against the Tokugawa, who had opposed the actions against the foreign nations and now fought for their own rule but eventually succumbed to the power of the revolution.
Support for this movement had come from the Western powers, that had supplied weapons and advice.
The winning factions of this struggle, which ended on January 3rd 1868, with the resignation of the last shogun, announced the Emperor to be once more the sovereign head of the state. Mutsuhito, the young emperor that had come from Kyoto to Edo to take control over a state emerging from medieval backwardness into the light of future global power, announced his reign to be “Meiji” – enlightened government. Edo became the residence of government and Emperor, and was renamed Tokyo – “Eastern Capital”.

 The Meiji System 
The leaders of the revolution (now called a restoration), soon turned over their possessions to the emperor. By 1871, the feudal provinces were made prefectures, their lords became governors, and all the lines of power now ran to the Emperor.
It was this restoration, and an immediate bid for military power based on the Western nations’ examples, that saved the ancient nation from coming under the rule of imperialist forces as did China. British officers took to building the Empire a navy that would be capable of preventing further incursions like Perry’s. French army officers restructured the old samurai armies and molded them into an effective fighting force. Dutch engineers took to building necessary infrastructure that could support both the warships bought in Europe and the Armies build up at home.
Further European ideas and ideals came to the modernizing Empire. A justice system based on the French model, a system of education based on the American model, and a system of political liberty that was to be found in the still absolute though nominally constitutional monarchies in Europe. Freedom of expression and thought were not among those granted to the Japanese, and basing the educational model on America’s did not prevent the Japanese from introducing even the youngest children to the idea of supreme rule by the Emperor, without argument. Books favorable to democracy were banned, and parties with desires to adopt democracy were forced to abandon their wishes or be banned as well.
It was mainly the fact that the Emperor’s sacred status was guaranteed by the prefectural leaders that enabled political change, for these prefectural leaders did have certain power aspirations of their own. In 1881, the first parliament convened, and in 1888, the a constitution was adopted.

 Foreign Policy and Expansion 
Japan’s new status was emphasized by the Empire by spreading its might abroad. In 1878, it occupied the Ryukyu chain, with Okinawa as the new prefecture capital. Earlier, in 1875, the Kuriles to the north had been occupied to provide a puffer against Russian aggression.
It would be up to the Chinese to engage the Japanese in full-scale war for the first time. Both sides had been working to get Korea into their sphere of influence. China had the older standing relations, but Japan copied what it had learned from the Western nations and successfully pressed Korea to accept trade relations. It also forced upon the Koreans a bid for independence from their mighty Chinese neighbor, who had dominated the Korean peninsula for several centuries, and whose place Japan would then take. These moves behind the scenes eventually caused tension to rise to a level were nothing but war could follow.
Japan would be the victor of this war. It executed a surprise attack on a Chinese squadron even before the declaration of war, then continued to stand by the ground forces, supporting the successful campaign on Korean soil. In the single naval battle, off the Yalu, it succeeded in repulsing a superior but less well led squadron of Chinese ships and finally bottled up the Chinese fleet in its harbor of Weihaiwei. Japanese Army forces beat the Chinese on Korean soil, and eventually, a war-weary China gave in to its fate.
In the treaty of Shimonoseki, Japan gained Port Arthur, the Laiotung Peninsula and Formosa, and not the least international reputation and a heightened spirit of self-confidence. Russia, Germany and France, however, prevented the Japanese from taking the fruits of its victory. Russia leased Port Arthur and the Peninsula. Only Formosa entered the Empire.
This initial victory would be standing alone for long. As a new continental power, represented by a fatherly Emperor who had became more than a sovereign, it sent troops to surpress the Chinese uprising against the Western nations in 1900. Two years later, it signed a alliance with Great Britain. A nation unknown fifty years before had become the partner of the world’s most powerful nation.
And it took to exploit this new alliance. Its continental desires still were aimed at Port Arthur. In 1904, it surprisingly attacked the Russians at their new fleet base. It had aimed at a treaty that would keep Russia out of Korea, but Russia had dismissed all talk. Now, the Imperial Navy struck. Forces were landed and the siege of the harbor began. The Russian Fleet tried to escape and destroy the blockade forces, but was beaten back. The besieged fleet called for help, and Czar Nicholas sent the Baltic Fleet to relieve the Pacific forces. In October 1904, the new fleet left the Baltic, but before it could reach and unite itself with the Pacific Fleet, Port Arthur fell. The new fleet continued on, hoping to get into Vladivostok and form a fleet in being, if not more. 
But the Japanese caught the enemy in the straits of Tsushima, between Japan and Korea, and soundly defeated the Russians. Only a handful of fast light cruisers escaped; Japan had won an overwhelming victory against a superior enemy.
If there had been any doubt in the Western nations’ minds that there was a new force to be reckoned with, this war dispelled it all.
When World War One began in 1914, Japan was the primary power in the Far East. It possessed the whole of Korea and Formosa, the Ryukyu’s, the Bonins, and was able to exercise its power anywhere its fleet would go.
Thus, not surprisingly, the possibility of gaining more territory at low cost made the Great War a welcome opportunity. Posing an ultimatum on Germany that demanded the Kaiser to cede its possessions in China and the Pacific to Japan, the Empire made sure that it would get those territories one way or the other. When the Kaiser refused to cede, Japanese forces took few months to occupy Tsingtao, the Marianas, the Palaus, the Carolines and the Marshalls. It did not participate to a great extend in anything else; and with the end of the Great War, it retained all the captured areas with the exception of Tsingtao.

 The Parliamentary Phase 1920 – 1941 
The 1920s were the most liberal phase yet in Japanese history. The nation, pretty much settled in its enlarged empire, still harbored imperialist sentiments, but for the moment, sensible leaders grasped that the time for expansion abroad had come to an end. With the Anglo-Japanese treaty running out and the Great War over, Japan was bound to face the full wrath of the Western nations should it attempt to do anything foolish. It thus accepted the invitation to the Washington Arms Control Treaty of 1921 – 1922, which settled the fleet ratios that Japan would be allowed to have vice sit more powerful Western opponents, and gave the island empire a measure of security that it had never before had. Although this was not what most of the ultra-nationalist factions thought, this treaty and it alone guaranteed Japan the option of deciding for or against war.
The period between 1920 and 1941 was the one with the most democratic type of government until after WWII, and yet it had severe flaws. It has been characterized as a “government by assassination”, so often were Prime Ministers, even lower ministers, the targets and victims of terrorist attacks that, instead of waiting for the next elections, chose to change the government in its own way.
Neither parliament nor government, to an extend not even the  Emperor, controlled the military. On the contrary, it was the military that controlled the civilian government. The Japanese constitution, more to the point several later amendments, explicitly required the ministers of the Navy and Army, respectively, to be serving officers of their services. By refusing to nominate a minister, either service could decline to accept an elected government. By removing its minister, either service could topple an existing government. It was thanks to the leadership of a few individuals that survived as Prime Ministers that any form of government could be executed without too large interference by the armed services.
As it turned out, matters were even worse – not even the Army itself could control its occupation forces in Korea.
To a certain extend, the events immediately leading to war with the U.S. for the results of events beyond Tokyo’s control.

 The Pacific War 1931 -- 1941 
In 1931, the Kwantung Army, responsible for the defense of Korea, plotted to topple the Chinese control over Manchuria. Army engineers blew up part of the Manchuria railway – only enough to blame the Chinese, not enough to do harm. Trains passed the area not long after, bringing troops into Manchuria. 
In Tokyo, the government was furious at first; law called for the most severe punishment for this open act of aggression towards a foreign nation. Yet Tokyo was also presented a huge area to control, on a silver platter for the Kwantung Army had already occupied the area that China had once controlled. The defunct empire of the Middle, split in internal fighting, did not oppose the Japanese.
It became an easy choice for the civilian leadership. It avoided a confrontation with the Army and claimed Manchuria as an “independent state” – Manchukuo, under a puppet  king placed in reign by the Japanese.
With its choice, the government had made itself an enemy of China, and a puppet of an Army that would not be satisfied by Manchuria or Korea – or China, for that matter.
The Kwantung Army kept moving. It occupied the Jehol province, to the north of Port Arthur, and moved into inner Mongolia. Chinese enmity meant little – the forces of Nationalist Chiang Kai-Shek and Communist Mao Tse Tung had their hands full fighting each other and would not allow themselves to be disturbed by the event on their northern borders.
In 1933, after being accused of cruelties against the population of Manchuria, Japan had removed itself from the League of Nations. It was only the first step in a dangerous collision course with the United States.
The traditional party governments had already been replaced by “governments of national unity” when Japan made the last step to full-scale war with China. At the Marco Polo bridge in Shanghai, on May 15th 1937, which housed considerable Japanese forces, Japanese and Chinese troops exchanged fire. The government of Prime Minister Konoe decided to punish the Chinese. Expeditionary forces occupied the northern and eastern Chinese shores, including the capital of Nanking, but China refused to surrender. Konoe, hoping to be able to control the Army in this war, failed badly. Soon, the Army was moving on its own, supported by a Navy that had a chance to sharpen its blade in actual combat.
A year after the incident, Prime Minister Konoe declared a “new order” for South-East Asia. It was sort of the Japanese “manifest destiny” phase, yet Japan did not intend to bring the people it occupied anything but occupation – Japan was to be the supreme ruler of all Asian people.
It was the developments of 1937/38 that compelled the U.S. government under Franklin Delano Roosevelt to support the Chinese against the Empire of the Sun. The U.S. demanded the Japan withdraw from China and leave it alone. When Japan failed to comply, the government being completely unable to exercise control over the military without facing personal danger of the gravest sort, Roosevelt terminated trade with oil and scrap iron.
Konoe, desperate to avoid war with the U.S., sought agreement over the China “Incident” (as the Japanese desired to call it) , but failed. Pro-China sentiments within the U.S. were too great for Roosevelt to accept anything than total removal of all forces from Chinese soil, and Japanese commitments to the war were too great to abandon it.
In 1940, the government of Konoe made its gravest blunder. By signing the Tripartite Pact with Germany and Italy. Allying himself so obviously with the fascist powers of Europe could not help Konoe’s cause for peace with the U.S.
With the fall of France, the military voted to occupy French Indo-China, which it did in July of 1941. In October of that year, a beaten Konoe resigned from his post. His best efforts to contain the military by letting it have its war, and then, by trying to fulfil its wishes without going to war with the U.S. had not succeeded. The U.S. froze all banking accounts of the Japanese government in the U.S.
Konoe was replaced by Army Minister General Tojo Hideki, who had been chief-of-staff of the Kwantung Army by the time of the Manchuria Incident. Under his command, the plans that Army and Navy had harbored for a south-ward advance, war with the U.S., and the establishment of a Greater East-Asian Co-Prosperity Sphere would be executed.

Bibliography
DTV-Atlas zur Weltgeschichte Band 2
Evans, David C. and Mark E. Peattie, Kaigun: Strategy, Tactics and Technology in the IJN 1887 -- 1941
Hall, John W., Das Japanische Kaiserreich Volume 20 of Weltbild Weltgeschichte
Ienaga Saburo, The Pacific War 1931 – 1945
Pemsel, Helmut, Seeherrschaft