Beginning in the early 1960s the new educational doctrine was installed, not only in the USA, but all over the western hemisphere.
The main focus of this programme seems to have been on set theory (much influenced by Nicolas Bourbaki and his works), functions and diagram drawings. It was stressed that these subjects should be introduced early.
Some of this focus was exaggerated. For example, first-graders were taught axiomatic set theory in some cases. The idea behind this was that if the axiomatic foundations of mathematics was introduced to children, they could "easily" cope with the theorems of the mathematical system later.
Tom Lehrer wrote a satirical song named New Math making fun of the more absurd aspects of New Maths.