Gold, God, and Glory. They went to the new world, America, so they could find new materials, gold being one of them. Then they used Religion as a smoke screen, covering up the real reason why they were there, to steal and obtain gold. They acted as if they were attempting to convert the American Indians over to Christianity. And then glory, they wanted to be praised because of their adventure to the new world.
Im pretty sure its true but not 100% correct .
Just a couple things
diseases that affect them during pregnancy
birthing troubles
possibly cultural or religious traditions that would make it hard for them to survive.