Why does the Pledge of Allegiance have "...Under God..." in it and why does the dollar bill have so many Christian references when the USA has no official religion?
Why does the Pledge of Allegiance have "...Under God..."
Because Catholics in 1951 decided it should be added and eventually convinced congress to amend it.
why does the dollar bill have so many Christian references
Specifically referring to "in god we trust", like the Pledge of Allegiance, a group of people decided to lobby the powers that be to add it. This happened during the civil war.
In other words, democracy. It just happens that--at least at the time of these changes--we were a democracy with a lot of Christians.
There has always been a tension between religious freedom and groups who feel that part of religious freedom is imposing their religion upon others.
However, if you'll note the timeframe when all of those things were officially added, it was during the height of the Cold War and anti-Communist hysteria in the USA. Those references were less about true faith and more about overty differentiating "God-fearing" Americans from the "godless" Communists.
A law passed in a Joint Resolution by the 84th Congress (P.L. 84-140) and approved by President Dwight Eisenhower on July 30, 1956, declared "In God We Trust" must appear on American currency. This phrase was first used on paper money in 1957, when it appeared on the one-dollar silver certificate.
In 1954, in response to the Communist threat of the times, President Eisenhower encouraged Congress to add the words "under God," creating the 31-word pledge we say today.
In general, religion is a big topic in the USA because many people immigrated to the USA came in order to have religious freedom.
I think they have no official religion because of the religios diversity in their country.