Attack on Pearl Harbor
The Attack on Pearl Harbor was a major event in World War II and marked the moment America became actively involved in conflict after Imperial Japan launched a surprise attack on Pearl Harbor on December 7th, 1941; utilizing what would become infamous as "Kamikaze" suicide-tactics.
The Attack on Pearl Harbor (which resulted in the loss of 2,403 American servicemen and 68 civilians) was effectively a declaration of war and began what would become a brutal battle between America and Japan - as well as the other countries in the alliance that would become known as the Axis Powers. America joined the war specifically one day after the attack.