Japanese culture is very unique compared to the rest of the world, particularly because of the country's long history.
With many similarities to the West, Japanese imperialism differed from Western imperialism in that it was the first non-Western imperial power, and that it rose to imperial status after facing colonization by the West. Like Western powers, Japanese expansion was fueled with Social Darwinism, and racism.
The era you're referring to however, began near the end of the rule of the Tokugawa Shogunate in the closing days of the Edo Period and ended with Japan's defeat in WWII during the Showa Period. Essentially from the 1870s to 1945.
Despite Japan's civilization, Western countries, because of racism, treated it the same way as other Asian countries.
Imperial expansion the last chance to win Western respect and ensure security and survival as a nation, and even bring civilization to other countries in Asia.
Imperial expansion went hand in hand with growing Japanese nationalism.
It's incredibly similar to every other great empire in history and of course we all know how that ends.
When Emperor Hirohito ascended to the throne in 1926, Japan was enveloped in a struggle between liberals and leftists on one side, and ultraconservatives on the other. In 1925, universal male suffrage was introduced, increasing the electorate from 3.3 to 12.5 million. Yet as the left pushed for further democratic reforms, right-wing politicians pushed for legislation to ban organisations that threatened the state by advocating wealth distribution or political change. This resulted in 1925’s ‘Peace Preservation Law’, which massively curtailed political freedom.
Again, we see many similarities to the west and particularly the United States during this same time period as part of the red scare, examples being Gitlow v. New York and the Sedition Act of 1918.
In July 1937, Japanese soldiers at the Marco Polo Bridge on the Manchuria border used explosions heard on the Chinese side as a pretext to invade China. The offensive developed into a full scale war, blessed by Hirohito. Japan enjoyed military superiority over China. The army advanced quickly and occupied Peking. By December, the Japanese had defeated Chinese forces at Shanghai and seized Nanking. There Japanese troops committed the greatest atrocity of an incredibly brutal war: the ‘Rape of Nanking’, in which an estimated 300,000 civilians were slaughtered.
This actually marked the beginning of end for the Japanese.
By 1939, the war was in stalemate; Chinese Communist and Nationalist forces continued to resist. Yet Japanese imperial ambitions were undimmed. In 1940, Japan signed the Tripartite Pact, creating the Rome-Tokyo-Berlin Axis, building on the alliance created in 1936 by the Anti-Comintern Pact. Japan now looked hungrily towards the oil-rich Dutch East Indies to fuel its Co-Prosperity Sphere. In 1941, when Imperial General Headquarters rejected Roosevelt’s ultimatum regarding the removal of troops from China and French Indochina, the US President announced an oil embargo on Japan. For Japan, the move was the perfect pretext for war, unleashed in December 1941 with the Pearl Harbor attack.
Due to Japanese culture and tensions with the west created by what the Japanese essentially viewed as insults, combined with an incredibly nationalistic population, the Japanese launched the pearl harbor attacks and finally gave the Americans the justification they had been searching for to enter the war.
They lost because they picked a fight with the wrong enemy(s) and thier empire fell because of it.
Nationalism, greed, and power are generally the reasons for the rise of imperialism, though the US is unique in the sense that even though it's called something different in the sense that it's driven by capitalistic profits. Generally, the only people that benefit from American imperialism are those at the very, very, top.
Japan's expansion may also be viewed as a way of competing with rival western nations and trying to find a place as a major power in the world.