Rapid expansion continued throughout the 1870s, 1880s. In 1881, the US bought out the British commercial venture that had been attempting to build a canal in Panama for years. The massive amount of US investment, importation of US workers and immigrants, and the fact of US commercial ownership of the canal that they built, had the UK agreeing to allow Panama to join the confederation in exchange for perpetual canal rights where British vessels would never be charged tolls. Panama was also mostly english speaking as it had been under British rule since 1814.
Meanwhile a rapid succession of new states in the Great Plains and Pacific Northwest joined the confederation including Dakota (November 2, 1889) with its capital at Bismarck, Montana (November 8, 1889), Idaho (July 3, 1890), Wyoming (July 10, 1890). In addition, the US annexed Hawaii in 1893 after the monarchy had been overthrown by settlers who had originated from the United States. Cuba also agreed to join the confederation (February 24, 1895), in exchange for the US agreeing that Spanish would become the third Federal language, able to be used in all parts of the Federal government and in Parliament. (in addition to French and of course English) Utah joined the confederation soon after that (January 4, 1896) having resolved its polygamy issues with the federal government.
The fourth and final founding father of the United States is generally considered to be Theodore Roosevelt, prime minister from 1903-1913. He oversaw the final completion of the Panama Canal, quickly considered an icon of the nation in 1903. Not long after that Panama joined the confederation (November 3, 1903). However Roosevelt’s signature achievement has been considered the rebuilding of the US Navy that had been left to stagnate after the wars of the 1850s. It was the navy’s subsequent tour of the world that increased the world’s recognition and familiarity of the US as a nation, increasing its profile where it had previously been seen only as an extension of Britain or British North America. Countries in Europe, Asia, South America subsequently recognized US power and independence due to the power and impressive size and modernity of its Navy. Roosevelt’s charisma and showman attitudes also made him world famous and placed the US firmly on the map.
However it was not to last as Roosevelt’s successors as prime minister embraced isolationism once again as the US contrived to stay out of all wars, the Navy was left again to languish as a consequence. But there was still much lasting impact as a result of Roosevelt’s actions. The US soon established official diplomatic relations with many of the world's powers and opened up foreign embassies for the first time in numerous countries, and received numerous ones in Washington in return.
Roosevelt’s tenure also saw the admittance of Saskatchewan (September 1, 1905), Athabasca (September 1, 1905, the local residents having rejected Alberta as being too pro-British and not reflecting who they were), Oklahoma (November 16, 1907), New Mexico (January 6, 1912) and Arizona (February 14, 1912).
However Roosevelt’s successor Woodrow Wilson was a staunch isolationist, elected after public fears of an arms buildup in Europe would lead the US to war in support of Britain. Prime Minister Wilson had campaigned to do all he could to prevent the US from being dragged into an European war and had won in a landslide.
This victory came as a real shock to Britain and served to wake them up to the reality. Britain had always thought that Germany would not declare war on France and thus Britain due to the factor of the immense United States. But unknown to Britain and the United States, Germany had plenty of agents in the US who reported back convincingly that the country would not likely support involvement in an European war. And so they had ramped up tensions in an arms race while Britain had fallen behind, thinking to depend on the United States. In reality Wilson’s victory should not have been seen as unexpected. The demographics of the United States had changed immensely since the 1850s when the US had supported Britain in the Crimean War not to mention the 1810s for the Napoleonic Wars. Much of immigration since 1850s had been Germans, Scandinavians, Irish, then Italians and East Europeans, not to mention Chinese/East Asian in the Pacific Northwest and the new Spanish speaking populations of the Caribbean states and territories. And these new immigrants easily outnumbered English ones, or at least those who still regarded themselves as English or British in identity and were loyal to the Crown.
So this led to the shock of 1914 when the US at first announced its total neutrality in WW1. Being an independent nation that was only under personal union to a constitutional monarchy, it had every right to do so. However Britain immediately dispatched diplomats to Washington arguing and lambasting Wilson for all that Britain had done for the United States, they deserved a bit of loyalty, ect, ect. Constrained by democratic reality, Wilson adamantly refused to join the war against Germany even as the Atlantic seaboard states were protesting in favour of a war declaration. In the end the two sides came to an agreement. Britain would cede the Bahama Islands (which included the Turks and Caicos Islands), Bermuda, and the British Virgin Islands (folded into Porto Rico Territory). So the US gained two new territories in the Bahamas and Bermuda. In return the US agreed to supply massive WW1 aid with the expectation that it would not be paid back. US made artillery, shells, firearms, machine guns, ammunition would begin pouring in, in exchange Britain would supply the design blueprints as to what it wanted the massive US industry to make. In this way, the US would modernize its own military manufacturing process. This was in addition to non-military supplies like agricultural products, boots, uniforms, helmets, ect that the US would supply to Britain. The US would not participate in anti-submarine warfare to patrol the Atlantic as Britain wanted. Woodrow fearing being drawn into war with Germany over the massive aid to Britain demanded that the UK would have to ship the weaponry and supplies back to Europe themselves, on US built convoys and destroyers.
In all, Nova Scotia, New England, Maryland, Virginia, Pennsylvania were the most enthusiastic for war. New York, New Jersey were ambivalent and split due to a new influx of immigrants. The Midwest was opposed, their historic ties with Britain had been mostly informal and they embraced isolationism and local identity first. And there was the factor of the large ethnic German population who would prefer not to get involved in any war with Germany.
The South had its loyalists (particularly Carolina, Texas, Kentucky, Tennessee), including many African Americans, but there were also those who resented crown interference in the past decades with regards to the issue of slavery and indentured servitude. Cuba was staunchly opposed to the war. Florida and Panama were pro-war. Canada was mostly opposed due to its perceived historical ill-treatment at the hands of Britain, as well as its large French speaking population.
All of the Western states were completely opposed and warned of secession if the US government should think to impose conscription which it constitutionally had no right to do.
WW1 lasted 1914-1919. In those years, US industry greatly expanded to meet British demand, but it was also fuelled by a rapid increase in US debt to fund and supply Britain’s war. And although the US was officially neutral, Britain did recruit 620,000 men (volunteers) to fight for the old empire of which 67,000 ultimately were killed and 250,000 wounded. In the meantime, Porto Rico (which included all of the Virgin Islands) joined confederation (March 2, 1917).
The negotiated Treaty of Versailles ended the war in 1920 after the ceasefire on November 11, 1919. Germany had forced the collapse of Tsarist Russia by late 1917, but their surge on the Western Front had ultimately failed to capture Paris, and by then Germany was on its knees due to the economic blockade leading to widespread starvation, there was famine and the growing menace of Communist revolution.