Why was the statement "In God We Trust" chosen as a national motto?

In God We Trust was added to the Latin saying E pluribus unum ("Out of many") in 1956 through a declaration by Congress.

The background to this decision was the Cold War and an effort to underscore the unity of the American people against the "godless communists". The declaration was initiated by the Dixiecrat and Congress member Charles E. Bennett, a member of the inner leadership circle of the anti-communist Christian fundamentalist network International Christian Leadership (ICL), which strives for a nation based on Christian principles.

In 1956, president Dwight D. Eisenhower, proposed the prhase "In God We Trust" as a way to reaffirm the importance of the religious faith, since he firmly believed that, by assuming it in every country practice, they should be able to strengthen the spiritual values over which the country was founded.