If the Russian-speaking population of Crimea and eastern Ukraine doesn't want to be ruled by Kyiv, how is that any different from Texas not wanting to be a part

If the Russian-speaking population of Crimea and eastern Ukraine doesn't want to be ruled by Kyiv, how is that any different from Texas not wanting to be a part of Mexico? > "The Mexican-American War was an armed conflict between the United States and Mexico from 1846 to 1848. It followed the 1845 American annexation of Texas, which Mexico still considered its territory..." (wiki) Of course it's equally clear Ukrainian-speaking western Ukraine wants nothing to do with Moscow, so this points to where a negotiated settlement could draw a new geopolitical boundary. Meanwhile, the USA has military forces in Syria supporting the Kurdish population, which doesn't seem to want to be ruled by Assad. How is that really any different (the geopolitical economics in that case appears mostly about not allowing Syria and Iran to cooperate economically and militarily, incidentally). Let's try to have an adult-level understanding of these conflicts, not the propaganda-for-gullible-children version of events and motivations.