Final answer:
Japanese militarism greatly influenced international politics from 1900 to 1945 by aggressively expanding Japan's empire in Asia, forming alliances with fascist countries through the Anti-Comintern Pact, and altering the balance of power that contributed to World War II.
Step-by-step explanation:
One significant way in which Japanese militarism affected international politics during the period of 1900-1945 was by challenging the balance of power in the Asia-Pacific region. The rise of militarism in Japan culminated in the country's aggressive expansionist policies, which resulted in the occupation and annexation of territories. Japan's military victories over Russia in the Russo-Japanese War and its continued expansion in Asia forced Western powers to recognize Japan as a major force. This led to a shift in global power dynamics, with Japan seeking to displace Western influence in Asia and create a new order under Japanese hegemony, particularly through the concept of the 'Greater East Asia Co-Prosperity Sphere' motto.
The militarists' control over the government also saw Japan allying with other fascist nations, notably through the Anti-Comintern Pact with Germany in 1936, and later Italy, paving the way for the Axis powers' formation. This alignment contributed to the tensions leading up to and during World War II. Moreover, Japanese imperialism's aggressive push in the Pacific region provoked responses from other nations, notably the United States, which eventually led to the Pacific Theater of World War II following the attack on Pearl Harbor. Hence, Japanese militarism not only transformed Japanese society and politics but had a profound and lasting impact on international politics during the first half of the 20th century.