The reason why Southerners were more likely than Northerners to support the Mexican-American War is because an American victory in the war would lead to more territory in the South being gained (territory once belonging to Mexico).
We can only theorize about how the life would be if the humans appeared earlier on the Earth, as we can not create a perfect and accurate picture of how would the things have been.
If the humans were developing in the same manner as we had, than we can say that the humans would have been much more advanced. The technology would have much better, probably missions to the other planets would have been regular. The population would probably be higher, with most of the population being concentrated in highly advanced megalopolises.
The environment though would probably be in a terrible condition, with enormous loss in biodiversity across the globe, decline in the forests, and much emptier (with life) oceans. On the other hand, there's every chance that with the more advanced technology multiple animals and plants would have been resurrected, even some extinct very long time ago.
Individual resistance to morally corrupt governments
