At least for the Aztecs, this is in fact the case. The Aztec kept subjugated peoples alive to husband them to supply human beings for their sacrifices.

The Spaniards allied themselves early with these would be victims, who therefore helped remove the numeric superiority the Aztecs would have otherwise enjoyed.

These allied tribes (see the Tlaxcala) then became a privilege class among the natives.

The guns, and the horses, obviously helped - but we're talking 4 orders of magnitude advantage if the Spaniards had not allied themselves with the locals. Even pandemics cannot erase that advantage (and they take time to spread)

> I wonder if this kind of customs helped the Spanish conquest and subsequent colonization of the Inca/Aztec Empire.

I don't think so. It's probably mostly down to what Jared Diamond describes - Guns, Germs, and Steel.

The occasional score of children and conquests slaughtered voluntarily is dwarfed by the numbers of natives that died from smallpox (f.e.).

Guns may have had much less to do with it than is commonly believed. I recommend the book 1492 if you're curious about why that is.

I tend to agree. I suspect the availability of guns was useful in a few key engagements, but the accidental weaponisation of smallpox (for example) was much more effective in wiping out indigenous forces.

Another thing to consider is that European guns sucked during that time period. Bows and arrows and other native weapons were probably very competitive.