When world war i began in 1914, which nation had an advantage at sea?

Britain had an advantage at sea during World War I.

Explanation:

During WWI, Britain had the strongest naval power among the other countries. There was a constant naval race between Germany and Britain, of which Britain was more advantageous in terms of sea- war and marine army. Sea power in the war was mainly dominated by the capital ships and battle cruisers having huge guns in it.

Despite of the constant competitive pressure from the German army, British army managed to have the largest naval army. Though British navy had numerous warships it still lacked the technological expertise of German navy. However, Britain was successful in weakening the German naval army.  

. political or economical policy that isolates a country from participating in international relationships. it has been suggested that the united states participates in isolationism because of its lack of involvement in particular wars or alliances.