In war, the decisions of individual soldiers make all the difference. 

After a successful attack on Pearl Harbor and invasion of south east Asia, the Japanese navy felt invincible. Yamamoto wanted to invade Midway to force a glorious naval battle with the Americans for supremacy in the pacific just 6 months after Pearl Harbor. Even tho he faced backlash from other military leaders, he forced their hand by threatening his resignation. 

In that battle they lose 4 carriers marking the beginning of the end.

Reading The Rising Sun by John Toland (highly recommend)