The correct answer to this open question is the following.
Although there are no options included, we can say the following.
European empires lack a workforce in the "New World" because they did not have enough European people or colonists that could perform the work needed to manage the new territories. They also did not have enough people to work the land. That is why they established the Encomienda system, very similar to slavery, in which Europeans such as the Spaniards force Native Indians to work for long hours in exchange for some food and a place to live.