What are the tiny invaders being discussed? Where are they arriving? Why are they arriving there?

there's multiple reasons why the conquistadors were so successful in colonizing central america, and some of them are:

- they were seen as gods;

at the beginning, the spanish settlers were seen by the natives as gods, and this was mainly due to their white skin, and the way they came with their boats.

- possessed superior weaponry;

the spanish had gunpowder and guns, as well as cannons, while the natives did not had any fire weapons.

- made cleaver alliances;

they used the situation of tribes hating each other, so they made alliances with some of them which served them very well.

- brought diseases;

the native people were not immune to certain diseases the europeans brought with them, so they were dying from seeming harmless things for european standards.