Original Answer: Because they are decades away.
Improved: The United Nations are not a country. They couldn't have "joined" the League of Nations. The League of Nations was the predecessor of the United Nations - the League of Nations failed, and so, many years later in 1942 (I believe it was that year) they founded the United Nations as an improved "League of Nations."
WW1. After WW2, the UN was created and anyone who was part of the League of nations joined the UN.
UN. the League wasn't joined b/c Wilson wanted to stay out of Europe's affairs
the league of nations was weaker than the UN because the united nations was stable UN like the league.
the leagueof nations and UN
Yes. It was the League before it became the UN.
It changed it became the UN. The UN is better than the league of nations.
The predecessor to the UN was the League of Nations.
League of Nations
The League of Nations was before the United Nations, then the UN was established.
The United Nations predecessor organization was the League of Nations which was founded at the end of WW1 as a result of the Treaty of Versailles and managed to attract at its best the participation of 58 countries during 24 September 1934 and 23 February 1935.
The United Nations, commonly reserved to as the UN.
Actually, UN is the successor of League of Nations. After the end of the league, i.e, after the outbreak of second world war, the members thought it was better to form a new world organization rather than reforming the League.That's how UN was created, and the UN wouldn't have existed if the league had. so there's no question of UN playing ANY role in the end of the League of Nations..!!!