Yes, the Mexican American residents of these territories did become U.S. citizens.
Stalin unified the Soviet Union after the death of Lenin, although it should be noted that this "unification process" involved mass killings and deportations of people Stalin deemed to be enemies of the state.
Answer:
The discovery of the New World by Christopher Columbus in 1492, although unexpected because he had never imagined that there could be a new land in his proposed journey towards the East Indies, had one pretty important reason, and it is told by the man himself in the letter that he sends to the Spanish crown and to his own financial supporter, Luis de Santangel.
The reason for this voyage, and the importance it had for Spain, was that commerce with the Far East, and with India, most importantly, had almost altogether stopped due to the blockade from the Arabs. The desire to find a new way to trade with the Asian continent, bypassing the blockade, encouraged first Portugal, and then Spain, to seek the sea as a means to achieve this. Columbus, an expert in cartography, believed that there was a way to reach India and thus proposed the plan to Luis Santangel and the Spanish crown. He received the go ahead and embarked on his journey. In the letter that he sends back, he clearly states the original reason for the journey, that ended with the discovery of these new lands, which he died believing were in Asia, was the need to re-establish commerce. However, later on he gives the Catholic monarchs, Fernando de Aragon and Isabella de Castilla, another reason to keep on with the project: he stumbles upon Natives, which he calls Indians, who would be open to Catholic evangelization, something that was very much in the heart if the Spanish monarchs. Thus, with these two reasons, more voyages are authorized by Spain, towards the newly found land.
