The Avalon Project at Yale Law School provides a transcription of the Northwest Ordinance. This created a legal structure within which the inhabitants of lands outside of the 13 original states could operate, outlined the steps to form territorial governments and the means by which new states could be admitted to the Union.
Documents Leading to Statehood
The Avalon Project at Yale Law School provides a transcription of the Laws for the Government of the Territory of New Mexico dated September 22, 1846 also known as the Kearny Code. An explanation of the international law at the time relating to conquest of land through war and treaties that follows are in two U.S. Supreme Court cases: Leitensdorfer v. Webb 61 U.S. 176 (1857) and Fleming v. Page, 50 U.S. 603 (1850).
In December 1845, the U.S. Congress voted to annex the Texas Republic which Mexico considered to be its territory and, after border skirmishes, Congress declared war on Mexico on May 13, 1846. Brigadier General Stephen W. Kearny was sent with troops to secure New Mexico, Chihuahua, and California.
The New Mexico Office of the State Historian provides this transcription of the Bill of Rights For the Territory of New Mexico as declared by Brigadier General Stephen W. Kearny, September 22, 1846.
This Library of Congress site has links to pages from the Treaty of Guadalupe Hidalgo, signed February 2, 1848 which brought an end to the war between the United States and Mexico. 525,000 square miles were ceded to the United States, including parts of present-day Arizona, California, Colorado, Nevada, New Mexico, Texas, and Utah.
This Library of Congress site links to Notes of a Military Reconnoissance [sic], From Fort Leavenworth, In Missouri, To San Diego, In California, Including Part of the Arkansas, Del Norte, and Gila Rivers. By W.H. Emory, Brevet Major, Corps Topographical Engineers. Made in 1846-7, with the Advanced Guard of the "Army of the West." (Washington, DC: Wendell and van Benthuysen, Printers, 1848).
The Library of Congress provides access to the Journal of the Senate of the United States of America, vol. 41, pp. 524-529 where the background is provided for amending the bill. S.
The Library of Congress provides access to President Millard Fillmore's December 13, 1850 proclamation "Declaring Act of 1850, ch. 49, respecting the Boundaries of Texas, to be in force" which was published on pages 1005-1006 of the appendix to volume 9 of the Statutes at Large.
The Library of Congress provides access to "An Act proposing to the State of Texas the Establishment of her Northern and Western Boundaries, the Relinquishment by the said State of all Territory claimed by her exterior to said Boundaries, and all her Claims upon the United States, and to establish a territorial Government for New Mexico" from the September 9, 1850 entry in the Statutes at Large.
This document is from a series of Library of Congress guides to "Primary Documents in American History" and shows how the creation of the Territory of New Mexico (which included Arizona) was part of the Compromise of 1850 which was an attempt to maintain the balance between the free and slave states in the United States and avert a crisis between the North and South.