Why were bodies of water like the Mediterranean Sea important to civilizations like ancient Greece and ancient Rome? How are they important now?

They were important due to trade.

Explanation:

The kingdoms of old needed trade to function. Land routes were not safe, so sea routes were to go. Sea routes were also faster. They now are important as quicker ways to transport massive amounts of cargo. Have you ever seen a building sized cargo truck before? you get my point.

The ancient civilization of Greece was located in southeastern Europe along the coast of the Mediterranean Sea. The geography of the region helped to shape the government and culture of the Ancient Greek.In brief, the importance of the Mediterranean Sea is conditional and its nature favors continental control; it is a sea of passage and a sea of land powers. ... Thus, for Britain, the Mediterranean Sea was a key link to India as well as a means of influencing economic dynamics within continental Europe.

since most of current immigration into the u.s., both legal and illegal, is coming from latin america. it would be very difficult to imagine or rationalize a country my fellow citizens are trying desperately to flee into, would pose a threat to my prosperity or freedom. since the u.s. has a long history of intervention, but no record of permanent occupation, i would not feel oppression is the main objective.  

the largest free trade nation, along with the largest gdp in the world wanting to expand it's economic policy on us, and including us, could only be positive. the u.s. government has no interest in, or way of simply forcing american culture on us. and has no track record of it. other nations that adopted american social culture, or "americanization" did so voluntarily, mainly through the choice of allowing american businesses and u.s. citizens to come into their nations, as free operatives.

the treaty of brest-litovsk was a peace treaty signed on 3 march 1918 between the new bolshevik government of russia and the central powers (german empire, austria-hungary, bulgaria, and the ottoman empire), that ended russia's participation in world war i.