Why has the United Nations not recognized Taiwan as an independent state?

The main reason is a dispute on whether or not Taiwan is a sovereign nation.

Explanation:

Only a sovereign nation can join the UN and China claims Taiwan is part of its territory and denies that Taiwan is a sovereign state. However, Taiwan is still vying for full membership.

The correct answer is to “to oppose the aggression of the axis powers including japan germany and italy”.

The WWII was going for some time before the US entered the war. It was after the Japanese attack on Pearl Harbor in 1941 that the US went into war.

There were basically two groups in the WWII. The Allies and The Axis. The Axis were mainly Japan, Germany, and Italy.  The Allies consisted of United States, Great Britain, France, and others countries, every country on the Americas declared war on the Axis.