"Great Britain policed, as far as anyone did, the oceans and seas, and it was the most important force in world finance, trade, and economy." Here, "as far as anyone did" seems hard to understand. Did "anyone" police the oceans and seas when Great Britain had the monopoly?
"Great Britain policed, as far as anyone did, the oceans and seas, - it implies that no country did very much policing of the seas, and that Britain did as much as any of them.
Most countries with sea-borders and navies run some kind of patrol to maintain their territorial rights and control piracy. The important factor is whether the country had a navy.