Once the spanish settled in mexico, their influence and population spread into today's california, arizona, new mexico, and texas. why?

a)the mexican population pushed them north, to stay further away from the capital.
b)the spanish wanted to claim as much of the new land as possible.
c)explorers warned the indigenous population of mexico not to travel to the north.
d) this land is in close proximity to mexico, easy to set up religious missions and villages.