Spain has found the new world (America) and quickly tries to make it their own. But there is one problem, Spain is not the only one wanting this new place, France is also wanting the same. So in order to make it their own they set down missions.
Spain wins Texas
Spain put down missions all throughout Texas. They used them because their other opponent the natives, knew the land better than them, so they thought they could give them their knowledge in order for the natives to help them out.
When Christopher Columbus found America, Spain wasn't the only place wanting it. France was also wanting to conquer this new place in order to expand their culture.
In the end Spain overtakes Texas and more parts of America. France wasn't able to support their forts because of the natives, and lack of resources.