I believe the U.N. motto to be from Isaiah 2:4, but I have not been able to find any solid evidence for or against that idea. "They shall beat their swords into powshares and their spears into pruning hooks." (and perhaps the rest of the verse) "Nation shall not lift up sword against nations, neither shall they learn war any more."
UN Day theme for 2011 :The united nations -in everyone's interest"
International Year of Human Rights Learning International Year of Reconciliation International Year of Natural Fibers International Year of Astronomy
International Year of Deserts and Desertification
1945
2002
1955
1946
1985
1965.
The Dominican Republic is a member country of the United Nations. The United Nations was established in October of 1945, and the Dominican Republic was one of the original members that joined that year.
International Year of Sanitation
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."
International Year of Planet Earth