Why did the United States drop two atomic bombs on Japan?

Basically to finally end the war.

Explanation: around this time of the war Germany had already surrendered  along with Italy, the only Axis power left in the war was Japan, the Japanese were cornered but did not surrender no matter how many lives were lost. The president then gave the order to drop the first atomic bomb on Hiroshima which devastated the city taking countless lives despite this the Japanese still did not surrender and so, a couple days after that a second atomic bomb was dropped which had finally made the Japanese admit defeat.