Return to Normalcy
The outbreak of World War I more or less completely halted immigration to both the United States and Canada for the duration of the war. British emigrants as a result, tended to choose either Argentina, Australia, or South Africa as their primary destination during that time period, as those regions weren't a conflict zone. Even Confederate immigration to the Union ended. As a result, the war actually led to a dramatic increase in the wage of American workers, as labor competition rapidly crashed. The formation of many labor groups, chiefly the Knights of Labor (which grew in size due to being seen as a "patriotic" organization agitating against the "Orientals") was rapid, as Knights of Labor branches sprung up across the entire nation.
This coincided with the inauguration of John Hay, who promised a return to normalcy. Peace had already been brokered by the Holmes Administration when Hay took office, so even his inauguration was taken as an example of normalcy returning. However, the Republican majority in the House and Senate (large in the House, narrow in the Senate) both came in with the belief that it was time to roll back the reforms of the Pennoyer/Holmes administration. Although their appointments to the Supreme Court couldn't be replaced, ending the era in which the Supreme Court used the privileges or immunities clause to strike down most economic regulations, they still exercised that power sparingly. The Hay Administration also moved carefully on the institution of an anti-trust act based on advice given by former President John Sherman. However, for the most part, the government refused to implement proposed economic regulations, siding with business against organized labor. The Knights of Labor were essentially treated as a branch of the opposition party.
Unionization had spread widely during the Pennoyer Administration as the government supported strikers, which made several states buckle down and promulgate laws recognizing unions. In response, the Hay Administration and the Republican Congress rammed a bill through Congress with the support of "Bourbon Democrats" led by figures like Grover Cleveland, which recognized unions federally and made it illegal to fire an entire union, but banned them from excluding non-union labor, while also making it very difficult for a specific individual to prove he had been fired for being in a union. A wave of strikes spread across the nation again, almost as large as the strikes that had created the Labor movement. The reaction of the federal government was to declare martial laws on railroads - and when a thrown bomb killed several Pinkerton agents, the Attorney General was ordered to directly prosecute "anarchists" for treason against the United States. Industrial violence skyrocketed as the Hay Presidency became known for violent labor-management struggles.
On the cultural front, there was relatively little fighting, as the Hay Administration tried to cleverly moderate on most such issues. For example, states were allowed to institute prohibition (and only Republicans did), but there was no national policy. The border states interestingly all kept alcohol legal, largely because the prohibition of alcohol in the Confederate States eventually created a psychotic smuggling ring centered around the Border States. Repudiating attempts to create a "Chinese Exclusion Act", President Hay himself bargained directly with Qing officials. In return for full resumption of trade relations and plentiful American investment, the Qing would strike a "Gentleman's Agreement" with President Hay to greatly greatly limit Chinese immigrants to the USA. This did not actually stop anti-Orientalism - since he was unable to reach a similar agreement with Japan, which continued to send immigrants, but it certainly weakened it, especially outside of the West.
Despite greatly frayed relations between the United Kingdom and United States, President Hay also rapidly worked to restore commercial relations with the United Kingdom. Refusing to pay reparations for the Vancouver Massacre, Hay correctly saw that the United Kingdom could more or less force Canada into accepting whatever terms both Washington and London agreed on - the Americans largely restored full diplomatic and economic relations with the UK, forcing the Canadians to comply as well. However, ethnic tensions simmered, especially in Maine, as the state government refused to allow expelled French-Canadian-Americans to return. "Minutemen" regularly patrolled the Maine-Quebec border in order to prevent "Papist infiltrators." Similarly, the United States government established direct diplomatic relations with the Vatican City, which outraged most of the Catholic World. Although President Hay went to great lengths to celebrate "patriotic Catholics" (aka, those that were part of the Union of Rome), most Catholic immigrants still stayed away from America.
The failure to conquer Hawaii was generally seen by President Hay as a repudiation of direct American imperialism, but it certainly didn't stop all American influence. Rather, it solidified the American sense that it should take stronger control of its direct colonies and areas of influence. President Hay, in a corollary for the peace deal that ended World War I, actually bargained fairly toughly with the British, achieving recognition of all Liberian land east of the Mano River, and making Britain agreed to support any American claims with regards to French Guinea. As a result, when the time came to negotiate borders between France and Liberia, the French largely gave up under combined UK-US pressure (neither side wanting to "poke the American eagle"), massively expanding Liberia's interior.
Of course, Liberia was actually an independent country, but that was not intended to stay true for very long. One group that suffered a great deal was American missionaries, who had traditionally seen China as the most fertile grounds for to proselytize. Although being fairly progressive in their political outlook, this was a generally a very loyally Republican demographic, ever since they flocked to the party to fight against slavery. World War I brought that to a complete end, as British missionaries quickly replaced American missionaries across China. By this point, Native American Indian communities had mostly been converted (well, to some degree - as most Native American communities had maintained self-autonomy, most Native Americans practiced a very syncretic Christianity) and integrated into the broader fabric of American society. The immediate effect of the defeat in the War of Southern Independence and the McClellan-Grant peace policy was an idealization of Native American culture in the West (outside of the Oklahoma ones, who were just seen as typical slaveholders), both in politics and art. This was only strengthened when the Native American tribes of the Dakotas were recruited to serve the US Army - generally being extremely successful in their raids against Canada (such as the famed severing of Canada'sTrans-Pacific Railroad by American cavalry working with Sioux warriors).
The President of Liberia, William D. Coleman, originally born from a slave mother and a white father in Kentucky, was facing serious opposition, both from progressives domestic politicians who opposed him for trying to expand Liberia into the interior (controlled by African tribes), opposition from conservative politicians who loathed his agenda of integrating and offering rights to native Africans, resistance from the tribes themselves, and fear that an expansionist France or Britain could roll them up. In many ways, he was looking for a lifeline - and the history of Santo Domingo offered an easy lifeline. Supported both by Republicans as well as interventionists in the former Anti-Oriental Party (the actual party had collapsed from infighting), the annexation of Liberia was approved despite protests from many American politicians and the vast majority of Liberia. The U.S. Army, which was not exactly a peacetime militia anymore (after World War I), but a ruthless, elite force, was shipped immediately across the Atlantic into Liberia to crush all opposition. Politicians across the Amero-Liberian Coast called for resistance, which was heeded by many progressive and most traditionalist Amero-Liberians (a small, but significant faction of progressive Liberians sided with America and Coleman). Coleman was expelled from the True Whig Party, which declared resistance. At every point, the Americans claimed they were enforcing the "lawful domestic order of a democratically ascended to the United States", trying to constantly disprove comparisons to Haiti. In reality, none of Europe cared much about either country. Liberia was in America's sphere of influence - and Europe didn't care what they did there.