I didn’t know that “under God” was added to the pledge of allegiance in 1954.
The Pledge of Allegiance was written in August 1892 by the socialist minister Francis Bellamy (1855-1931). It was originally published in The Youth’s Companion on September 8, 1892.
In its original form it read:
“I pledge allegiance to my Flag and the Republic for which it stands, one nation, indivisible, with liberty and justice for all.”
In 1923, the words, “the Flag of the United States of America” were added against Bellamy’s wishes, as he wanted the pledge to be used by any citizen of any country. At this time it read:
“I pledge allegiance to the Flag of the United States of America and to the Republic for which it stands, one nation, indivisible, with liberty and justice for all.”
In 1954, in response to the Communist threat of the times, and fifty-two years after its original publication, Eisenhower encouraged Congress to add the words “under God,” creating the 31-word pledge we say today. Bellamy’s daughter objected to this alteration. Currently there are Constitutional challenges to this alteration.
A more detailed article is here.