Russo-Japanese War
The Chinese Empire of the Qing Dynasty was large but weak, and it was Qing land and possessions they fought over. For example Korea was under Qing rule, but was seized by Japan. The Russians wanted a 'warm-water port' on the Pacific Ocean for their navy and trade. The harbour at Vladivostok freezes over in the winter, but Port Arthur (now part of Dalian on the Liaodong Peninsula in China) can be used all the time. Russia had already rented the port from the Qing and had got their permission to build a Trans-Siberian railway from St Petersburg to Port Arthur.