The attack on Pearl Harbor thrust the United States into World War II. The attack had significant and far-reaching political effects on the United States, changing the minds of many who had been philosophically opposed to war or who had taken a passive stance towards the war in Europe. The increasing diplomatic confrontations and economic sanctions against Japan by the United States and others, compounded by Japan's undeclared war in China and the weakening of European control in Asian colonies, precipitated the war in the Pacific. The Japanese felt that the time was opportune to conquer British, American, French, Chinese, and Dutch territories in Southeast Asia. This belief pushed militaristic factions in Japan to provoke war with the United States. Fearing that the United States Pacific Fleet would pose a formidable obstacle to Japanese conquest of Southeast Asia, Admiral Isoruko Yamamoto, Commander-in-Chief of the Japanese Combined Fleet, visualized a bold attack on the Pacific Fleet while it lay at anchor at Pearl Harbor. Such a surprise strategical attack, bold and daring in its execution, would, he believed, secure the Pacific.