As the European middle ages were ending Japan's Sengoku Period was beginning. After centuries of fighting the allied warlords Nobunaga Oda, Hideyoshi Toyotomi and Ieyasu Tokugawa emerged the winners. Their differing approaches were summed up as "If the bird does not sing, kill it" (Oda), "If the bird does not sing, coax it" (Toyotomi), "If the bird does not sing then wait" (Tokugawa). With the Emperor a mere figurehead since the beginning of the Sengoku Period, when Nobunaga was burnt alive by one of his retainers (Mitsuhide Akechi) Toyotomi succeeded him. While Oda had feigned interest in Christianity to get firearms from the Dutch (having far more guns than other armies is one of the major reasons why Oda rose to power) Toyotomi nailed his colours firmly to the mast with the crucifixion of 26 Christians in the southern port city of Nagasaki on the 5th of February 1597 (being where the Portuguese first arrived southern Japan and in particular Nagasaki is more Christian than the north). He did however attempt to carry out Oda's wish to conquer China but after initial success in Korea the invasion failed. After Toyotomi died his son's army, Tokugawa's and that of the Emperor (who like Hideyori Toyotomi also a young man who had recently arisen to this post after the death of his father) met at Sekigahara. The Emperor was unsure whose side to take until cannon fire by the Tokugawa army convinced him to support them which led to their victory and centuries of peace, but not for foreigners who were banned from Japan on pain of death and Christians whose religions (mainly Catholicism) were kept barely alive by disguising Christian figures as Buddhist ones. Japan settled into a period of isolationism the upside being peace and the downside being not knowing what was going on in other parts of the world Japan was unaware that it was lagging behind technologically. One of the more lasting legacies of this period is that Edo (now Tokyo) remains the capital of Japan having replaced Kyoto.
When the American Commodore Matthew Perry was sent with 3 warships to force Japan to resume trading with the west in the 1860's the Japanese overthrew the Tokugawa dynasty for failing to protect them and restored the power of the Emperor. The young Emperor Meiji then reformed Japanese society with the adoption of a Prussian style parliament (Diet) and army, a British inspired navy and teachers from France and the United States and Christianity could once again be practiced. With the rapid modernization was an immense industrialization and the Emperor's forces defeated the samurai rebels but the samurai would get many top positions.
China had been the dominating power in east Asia for centuries, but with better technology, weapons, and leadership the Chinese, were easily beaten in less than a year in the First Sino-Japanese War (1st August 1894 - 17th April 1895). Japan officially became a superpower and the most powerful in Asia. Japan was even able to challenge other superpowers, most notably Russia, which succumbed, to most people's surprise, in less than 2 years in the Russo-Japanese War (8 February 1904 - 5th September 1905). Fascists gained control of Japan's government leading to Shintoism becoming the state religion and the invasion of China in 1935. In response to this the United States cut off Japan's oil so Japan launched a simultaneous invasion of the rest of Asia and attack on the US naval base at Pearl Harbor on the 7th of December 1941 although the victory was not as complete as it could have been with the US carriers at sea and not in Pearl Harbor. Japan won stunning victories on land and at sea but their code was cracked leading to a heavy defeat at the Battle of Midway followed by more and Japan's eventual surrender after a nuclear bomb was dropped on Hiroshima and then Nagasaki resulting in tens of thousands of deaths and decades of radiation and its assorted side effects. Japan finally surrendered, putting an end to Japanese Aggression.
Japan After WW2
The US occupied Japan and introduced reforms to the nation, such as free-market capitalism and a democratic government. Its goal was to change Japan in a way that would prevent any more Japanese Aggression in the future. After World War II ended the conservatives easily won the election as they have at nearly every Japanese election since. As with other participants in World War II Japan's economy had multiplied in strength by the 1960's. In the 60's there was much tension between left and right; the socialist leader Inejiro Asanuma was nototriously killed on live TV by a fascist. After Israel's victory in the brief Yom Kippur war (6th - 25th of October 1973) the Arab countries reduced their sales of oil to other countries leading to an energy crisis and economic decline. Nearly out of oil, the Japanese government took an interest in Arabic culture and the oil then flowed more freely allowing Japan's economy to recover. In the 1980's there was record levels of student violence with the generation who knew only the prosperity of 1980's Japan and the generation who had lived through the hardships of World War II unable or unwilling to understand each other. After peaking the violence then declined year on year. With low interest rates borrowing and spending increased during Japan in the 80's and some even predicted that it would become the world's top economy, toppling America but this didn't happen and in 1991 the bubble burst and Japan has had economic troubles, most notoriously a high level of debt, ever since. In the 90s, Japan experienced more trouble after a terrorist attack on a subway station.
Despite such troubles, the 90s saw the creation/growth of many world popular franchises originating in Japan. Manga and anime series, like Sailor Moon created by Naoko Takeuchi Dragon Ball Z created by Akira Toriyama emerged while hit video games like Pokémon created by Satoshi Tajiri and Super Mario Brothers created by Shigeru Myiamoto debuted.
It is said that the Japanese are born Shintoist, have a Christian wedding and a Buddhist funeral. While only 1% of the Japanese are Christian about half of Japanese people have a wedding which is Christian in terms of aesthetics (a foreigner acts as the "priest" in a church looking building) if nothing else.