On this 28th day in December of 1945 the United States Congress Officially Recognized the Pledge of Allegiance. The words Under God were added on Flag Day 1954.
Here's a Timeline:
August 1892 - Pledge written by Francis Bellamy.
September 1892 - Pledge published in the Youth's Companion.
April 1898 - NY passes 1st law requiring recitation of the Pledge, in schools.
1923 to 1924 - National Flag Congress authorize words changed from, "I pledge allegiance to my flag" to "I pledge allegiance to the Flag of the United States of America.
June 1942 - the Flag Code becomes law (77th Congress)
June 1954 - President Eisenhower signs bill to include "Under God".
There's much more history to this whole evolution of our Pledge of Allegiance. These posted are the highlights.
Source: History of the Pledge Allegiance | Preceden