Hi passerby,
If one is wondering how fast the new missile is, or if the 4,200 miles is curvilinear or straight distance, or can this missile travel further down the equator, I think 'Chrisss' can explain them better.
I don't know too much about this missile (if it is new or a new variation of an existing missile). However, the Minutemen III missiles previously had a range of more than 8,000 miles (13,000 km). These are strike distances (i.e., launch versus strike target) and not travel distance. So, it travels further on its trajectory than its striking distance because it can rise 700 miles and then descend to its target.
In fact, the upper distance of the Minutemen III is a bit higher when it travels westward because of the way that the Earth spins on its access. The missile can rise up to an altitude of 700 miles (whereas the Karman line edge for "space" is 62 miles while real "space" is generally regarded as about 73 miles/118 km). Since the earth rotates on its axis at roughly 1000 mph (from the west), the distance is expanded. I'm not sure if the maximum range includes the rotation of the Earth.
Typically, the military tests these missiles for purposes of testing new propulsion systems, the accuracy of new trajectory systems, as a "statement" launch (reminding other nations of military strength) as well as for purposes of diversion (i.e., military operations in the area to "review" the launch but actually there for a different reason).
I don't think that the people living in the area were in real danger. In this day and age, the U.S. military certainly wouldn't want the bad press for a failed test or a fatality.