Before 1890, American lands consisted of little more than the contiguous states and Alaska. By the end of World War I, America could boast a global empire. American Samoa and Hawaii were added in the 1890s by force. The Spanish-American War brought Guam, Puerto Rico, and the Philippines under the American flag. The Roosevelt Corollary to the Monroe Doctrine declared the entire western hemisphere an American sphere of influence. Through initial negotiation and eventual intimidation, the United States secured the rights to build and operate an isthmathian canal in Panama. The German naval threat in World War I prompted the purchase of the Virgin Islands from Denmark in 1917.
Of the history of the indigenous population of California , Sherburne F. Cook (1896–1974) was the most painstakingly careful researcher. From decades of research he made estimates for the pre-contact population and the history of demographic decline during the Spanish and post-Spanish periods. According to Cook, the indigenous Californian population at first contact, in 1769, was about 310,000 and had dropped to 25,000 by 1910. The vast majority of the decline happened after the Spanish period, during the Mexican and US periods of Californian history (1821–1910), with the most dramatic collapse (200,000 to 25,000) occurring in the US period (1846–1910).   
Meyer , along with Pierce v. Society of Sisters (1925), is often cited as one of the first instances in which the . Supreme Court engaged in substantive due process in the area of civil liberties . Laurence Tribe has called them "the two sturdiest pillars of the substantive due process temple". He noted that the decisions in these cases did not describe specific acts as constitutionally protected but a broader area of liberty: "[they] described what they were protecting from the standardizing hand of the state in language that spoke of the family as a center of value-formation and value-transmission...the authority of parents to make basic choices" and not just controlling the subjects one's child is taught.  Substantive due process has since been used as the basis for many far-reaching decisions of the Court, including Roe v. Wade , Planned Parenthood v. Casey , and Lawrence v. Texas . Justice Kennedy speculated in 2000 that both of those cases might have been written differently nowadays: "Pierce and Meyer, had they been decided in recent times, may well have been grounded upon First Amendment principles protecting freedom of speech, belief, and religion."