1) Form of government 2) Former empire 
The term thalassocracy (from Greek language θάλασσα (thalassa), meaning `sea`, and κρατεῖν (kratein), meaning `to rule`, giving θαλασσοκρατία (thalassokratia), `rule of the sea`) refers to a state with primarily maritime realms—an empire at sea, such as the Phoenician network of merchant cities. Traditional thal...
sovereignty of the seas
thalassocracy 1. Mastery or command of the sea. 2. The sovereignty of the sea: 'England's thalassocracy was chiefly responsible for her once-huge empire.'thalassocracy, thallassocraty; thalattocracy, thalattocraty 1. Naval or commercial supremacy over a large area of the sea or ocean. 2. Maritime supremacy; ruling the seas; the sovereignty of the seas; mastery at sea.