The name for this idea is "Domino Effect" - this is a theory that says that if one country falls to Communism the neighboring countries would also fall to Communism, much like pieces of Dominos fall when a neighboring piece fell.
This theory was important in the Foreign politics of the US during the cold war.
B. The English Channel helped protect the island nation of Britain from invasion.
Baldassare Castiglione wrote The Courtier during the Renaissance which described courtly conduct for the nobles of Italy. This is where we get the term Renaissance man.
