Reciprocal Anglo-American assumptions in war plans for Japan

British and American plans for war with Japan shared an important assumption. British planners expected the United States to join if Japan attacked British interests, while American planners expected Britain to join if Japan attacked the United States. Each feared that staying outside would weaken its own position if the other power defeated Japan and shaped the Far East alone. The state attacked first would therefore become the leading power in the coalition, making the order of Japanese attacks strategically important.