What brought the United States into conflic with Native Americans in the 1800s?

You may need a renewed passport. For Americans it would. I don't speak Italian to check their web sites for information, but the United States information applicable to United States citizens is below:

Spain is a party to the Schengen Agreement. U.S. citizens may therefore enter Spain for up to 90 days for tourist or business purposes without a visa. Your passport must be valid for at least three months beyond your date of departure from Spain. You need sufficient funds and a return airline ticket

https://travel.state.gov/content/travel/en/legal/Judicial-Assistance-Country.../Spain.html

https://www.cia.gov/library/publications/the-world-factbook/geos/us.html

https://factfinder.census.gov/faces/nav/jsf/pages/index.xhtml

http://travel.nationalgeographic.com/travel/countries/united-states-facts/

https://www.britannica.com/list/10-fascinating-facts-about-the-first-americans

Which area in the world are trying to find the information. There were a lot of camps

1. Many Americans believed U.S. had to expand or explode.
a. Increase in population, wealth, and industrial production demanded more
resources.
i. Some feared existing resources in U.S. might eventually dry up
ii. Panic of 1893 convinced some businessmen industry had overexpanded resulting
in overproduction & underconsumption
b. Labor unrest and agrarian unrest (Populism) rampant due to industrialism.
c. Overseas markets a possible safety valve for U.S. internal pressures.
2. The experience of subjugating the Plains Indian tribes after the Civil War had
established a precedent for exerting colonial control over dependent peoples. AMERICAN IMPERIALISM 1890 1913

Passage of the Immigrant Quota Act of 1921 and the National Origins Act of 1924, which limited the number and nationality of immigrants allowed into the United States, effectively ended the era of mass immigration into New York. From 1925 to its closing in 1954, only 2.3 million immigrants passed through Ellis Island-which was still more than half of all those entering the United States.
Ellis Island opened to the public in 1976. Today, visitors can tour the Ellis Island Immigration Museum in the restored Main Arrivals Hall and trace their ancestors through millions of immigrant arrival records made available to the public in 2001. In this way, Ellis Island remains a central destination for millions of Americans seeking a glimpse into the history of their country, and in many cases, into their own family's story.