Today, Puerto Rico’s economy is too fragile and its politicians too corrupt to function without the help of the United States; and what should one expect of a little island?

As a territory, Cuba would not have been as fragile by now as is Puerto Rico, due to massive tourist appeal, for one thing. The island also has significant reserves of nickel and cobalt, top five in the world for nickel by many estimates. In any case, I think you generalize too much about “experimentation”. Only so much can be done with small post-colonial regions. Costa Rica has far, far better institutions than Cuba and still it is relying on agriculture and tourism.

RE northern Mexico in 1848: Josiah Gregg, who was with the American army in northern Mexico, said that “the whole country from New Mexico to the borders of Durango is almost entirely depopulated.” That is close to exactly the Tropic of Cancer latitude.

You join those who frowned on Manifest Destiny (a condition of “then”, not “now”), but considering the fate of that country under the control of about a dozen criminal families following the so-called revolution (1910-1920), a development following the pattern of the other southwest states would have been preferable.

Your reference to “paying the price” means demographic stresses I suppose (with all the attendant racial rhetoric). Those would have been present in this century in the US in any case, as in Europe. There is always irony and paradox in social phenomena, especially on a large scale.