It's not the military that makes it impossible.

It's the incredible level of interwoven left/right, progressive/conservative, urban/rural populations in more or less every state.

More people voted for the current president in CA than in more or less any other state. Yet it is viewed as a "blue" state. The millions of Democratic voters in large cities like Houston or Atlanta may not control their state legislatures, but they are not going to sit by as those legislatures attempt to secede. Rural voters across most states are not going to sit by while their urban-controlled legislatures attempt to secede.

We don't have "peripheral" states here, and we don't have "red or blue" states. We have a mostly urban/rural divide that does not follow state boundaries in any sense at all.

It won't change until states nominally considered "red" or "blue" actually lose the vast majority of their nominally opposed population (e.g. Atlanta's current population migrates out of GA). Until then, just about every state is a complex mixture of populations with different political alignments and sufficient sizes to make secession extremely difficult if not impossible.

The "peripheral" countries mentioned in the GP were nations or at the very least distinct semi-national entities before the USSR.

States in the USA have no effective history before being a part of the USA.