its a little more complicated then that, sometimes there was some justification for those expansions, akin to fighting terrorists. At least that's what the official reason was for some Mexican incursions. To fight the banditos. Not much has changed in that regard, they are called Cartels now. And there was kind of a Cuba thing going on, with supposed foreign sponsored coups (kind of like Germany causing uprisings) and such.
i.e.
https://en.wikipedia.org/wiki/Pancho_Villa_ExpeditionBut in the end it kind of has that 'special military operation' vibe to it. But its important to know how they were BSing in Washington about these kind of things
Same thing that seems to happen everywhere, some brave settlers settle where they probably should not have settled and then some force terrorizes them (some rape, pillage, threats, etc) and then there is a over blown response due to lack of police/justice systems in the area , and then it escalates because two groups of politicians get some kind of information about it
https://en.wikipedia.org/wiki/Bandit_WarI think it would be very hard to get accurate information due to the intense amounts of 'yellow journalism' that all the major powers had going on around that time, which probobly lead to the world wars
It is interesting how ugly borders can be. Another one that comes to mind is the border between Albania and Yugoslavia during the cold war (two communist states). They had state sponsored 'banditos' too
https://en.wikipedia.org/wiki/Albanian%E2%80%93Yugoslav_border_conflict_(1948%E2%80%931954)
And of course you have the problems created by irregulars , i.e. 'bushwackers' in old terminology that were used to kind of like manage... not very populated or important territories during a time of war. The politicians officially settled a matter and then you had kind of extreme groups that had little communication and discipline who would keep doing whatever they were doing because it was profitable. During a time of war they got support and then when it ended you essentially had people with no skills that turned into a militarized mafia that ended up causing severe trouble and reigniting things... very similar to al quida or whatever other organizations you can think of but in the 1800's