What started the Russo-Japanese War? Russia issued a preemptive strike on Japan in the Sea of China. The conflict over Korea escalated into war near Seoul, Korea. Japan launched a surprise attack on the city of Port Arthur in Russia. Negotiations to avoid war broke down, and war ensued.

The main reason why the Russo-Japanese war started during the early start of the 20th century; it is regarded to be the first major conflict of the 20th century, was because Japan launched a surprise attack on the city of Port Arthur in Russia which was a direct provocation.

Explanation:

The Russo-Japanese War was contested between the Russian Empire and the Empire of Japan above rival supreme ambitions in Manchuria and Korea. The principal objectives of sections were the Liaodong Peninsula and Mukden in Southern Manchuria and the seas around Korea, Japan, and the Yellow Sea.

The main reason why the Russo-Japanese war started during the early start of the 20th century; it is regarded to be the first major conflict of the 20th century, was because Japan launched a surprise attack on the city of Port Arthur in Russia which was a direct provocation.