Fallout shelters are still someone in use but not for the purposes of nuclear fallout, only severe storms, etc. Th Interstate Highway System is the best choice from this list.
Answer:
<em>Indentured servants in the early 1800s were usually immigrants.</em>
It would interfere with their trade alliances.
Communism leads to the government taking control of resources and industry. If it spread into areas the US did business, they could lose the ability to control resources and trade. This would eventually impact our political power and any military advantages the US had in Europe.