The trade barriers above are all types of
a. economic conflicts created by wars.
b. natural geographical barriers to trade
c. agreements created by governments.
d. policies related to transportation,

here are some major conflicts i found. maybe pick one and do more research on it. (cause i ain't writing 6 paragraphs)

in 1877, the nez perce war took place.

1881 - president james garfield was assassinated.

1882 - the chinese exclusion act was passed.

1883 - a decision in the civil rights cases legalized racial segregation in the united states.

1887 - the dawes act was passed.

1893 - the panic of 1893 took place. (what a creative name)

and there are probably other topics you can find if you just search up "united states timeline," or "conflicts in the 19th century for america."

then once you find a topic you like find out how it affected the people of america and what not. (sorry if this feels a bit short changed, history was and never will be one of my strong topics)

united states reinforcements contributed greatly to three allied victories in france at: cantigny (first major american battle), argonne (the largest in the united states military history, involving 1.2 million american soldiers), and château-thierry (one of the first actions under general pershing).

there are many answers to this question, such as a diplomat, ambassador, soldier, united nations employee, cia, etc.