Outside Context Problem
It wasn't the Spaniards' technology or guns that defeated the Mesoamerican civilisations. Consider that the Spaniards had logistical problems (they had to ferry supply trains across the Atlantic, and the fact that the Mesoamerican people knew the terrain and had the home-ground advantage. Their Jaguar and Eagle warriors with their maquahuitl swords and effective bows and arrows were more than a match for the slow-loading Spanish musketeers and cannoneers.
Motecuzoma II, the Reverend Speaker or king of the Mexica people (who we today call the Aztecs) was an expansionist tyrant who had gone to war with a neighbouring nation, the Texcalteca, at the time the Spaniards arrived. At first, the Mesoamericans thought the Spaniards were the returning god Quetzalcoatl, but their behaviour quickly disabused them of that notion, and Mexica soldiers posed a serious problem to the newly arrived Spaniards.
However, the Texcalteca were losing the war against Motecuzoma (who the Spaniards called "Montezuma") and the Mexica, and so they agreed to aid the Spaniards against their enemies. It was their assistance and inside information that made it possible for Cortes to cross inland and see the Mexica capital, Tenochtitlan, for himself. He admitted, at the time, that the power and culture of these people was too great to overcome. But there was one factor that he - and the Mexica - failed to foresee.
What really won the war for the Spaniards, and ultimately the English, was the first-world diseases they brought over - notably smallpox, great pox, bubonic plague, measles, gonorrhea and syphilis - to which the Native Americans had no immunity. Some estimates show that as many as 80% of Mesoamerican deaths in the first century of Spanish colonisation were the result of these diseases, much more so than guns and horses. The survivors were too disfigured and demoralised to fight back, and the rest is history.
Had we not brought those diseases to America, or had they been immune, history would likely have turned out very differently. While the northern tribes were largely nomadic, the Mesoamerican people were an advanced city-building civilisation technologically on par with Europe at the time. They gave us many inventions we take for granted - indoor plumbing, the flush toilet, hydroponics, the list goes on. They lacked only the wheel, rideable animals and gunpowder. Not having the wheel makes them sound more primitive than they were; but the terrain they lived in was not conducive to roads or wheeled transport anyway, as the Spaniards found to their great cost. It was only with the greatest difficulty, expense, and lots of slave labour that the colonists were able to build trafficable roads through the region over the next few centuries.
So it's interesting to think what might have been if the Mesoamericans had not succumbed to disease - if they had driven the Spaniards back into the sea. Today's America would be a very different place, and seeing what uses the Mesoamericans would have put European technology to, as China and Japan did, would have made it a more interesting, and perhaps less generic, place.