When U.S. military strategists planned the invasion of Iwo Jima, they estimated victory within five days. The United States did not anticipate the Japanese strategy of under-ground bunkers and suicidal soldiers that held off American forces for over a month and caused a devastating number of casualties. Iwo Jima was a strategic outpost for both the Japanese and the Americans. It was part of Japan, and, until then, Japanese soil had not been successfully invaded in over 5,000 years. The Japanese did not want to hold on to Iwo Jima simply for pride or tradition. Japan knew that if the Americans captured the tiny island, they could mercilessly bomb Tokyo and other Japanese strongholds. Japan no longer had the men and the supplies to fight a massive war. Therefore, the strategy in Iwo Jima was more about delay than men or victory.