Becoming a U.S Citizen requires you to somehow migrate to the United States using a visa. The US Citizenship and Immigration work in common. The United States offers different categories of visas and they are grouped into the following:
Family-based: This Visa is given to the close relatives of a United States Citizen and legal permanent resident.
Employment-based visa; This Visa is given to those that are given permanent employment by United States Citizen or they have a viable business in the United States.
Inter-country Adoption visa: This Visa is granted to adopted children from other countries, be it orphans or non-orphans.
Special Immigrants visa: This Visa is for special categories like United States employees like Iraq translators
Investors visa: This Visa is approved for investors seeking to invest in the United States economy.
Any foreign Citizen that wishes to migrate to the United States must be sponsored by a United States Citizen or a legal permanent resident.
Migrating to the United States is just one part of becoming a citizen in the United States, becoming a citizen in the United States just like having a visa in the United States have different ways of going about it.
Citizenship by naturalization: This is the application to become a citizen by submitting a naturalization form after you must have met the eligibility requirements.
Citizenship by marriage: Citizenship by marriage requires that you have a spouse that is a citizen of the United States and you must have spent a couple of years in the United States with your spouse.
Citizenship by birth: A child automatically becomes a citizen of the United States if both or one of the parents of the child is a citizen of the United States. A child can also be a citizen of the child was given birth to outside the United States, so long there is a parent that is a United States Citizen.
Military Service: one can become a citizen of the United States of America by the Services rendered by the person as a military officer. It can either be in times of war or peacekeeping.
These are the basic US citizenship and immigration categories. Becoming a citizen of the United States requires you to have a green card unless for cases of asylum. Each of these ways of becoming a citizen has its own requirements to be met, and then there is a general requirement that is to be met also before application to becoming a citizen begins.