The United States was one of the first nations to contract colonial development of Mars, and was one of only two nations to already have territory claims prior to colonization with the regions explored by decades worth of robotic probes.
In 2039 the US became the first human nation to recognize an off-Earth colony as an equal state in the Union with the admission of Viking from the old Tharsis territory. By 2054 with the admission of Absaroka into the union every American territory on Mars had been admitted as a state. In 2072 with the creation of the Four-Tier Republic system Mars became the second Commonwealth (after Earth) to be consolidated.
This is part of a series I'll be doing showing the sub-divisions and some of the history of Mars in my Second Renaissance scenario.
For More check out: Terraformed Mars MapThe Outer ColoniesThe Inner ColoniesFuture Old Glory