Two policies presented themselves to the British government at the beginning of the war. They might have used their great naval strength alone, blockading the coast and sealing every harbor; thus the colonies would be cut off from the rest of the world, and allowed to enjoy their independence until they were ready to return to their allegiance. The alternative of invasion was chosen; but it was useless, with the forces available, to occupy any considerable part of the interior. By threatening various parts of the coast, the Americans could be obliged to make many detachments of their few troops. By occupying the principal towns, such as Newport, New York, Philadelphia, Charleston, and Savannah, the centres of resistance could be broken up, the loyalists encouraged, and bases established, from which the main American armies were to be reached and destroyed. On the sea the navy was to be used to ruin American commerce and to prevent the importation of supplies. [Sidenote: American military policy.] The policy of the Americans was, not to attempt to defend the whole coast, but to keep as large a number of troops as they could raise together in one body, as a substantial army; to defend their land communication from New England to the South; and by standing ready for operations in the field, to prevent the British from making any large detachments. They must hold as much of their territory as possible, in order to prevent defections; and they must take every advantage of their defensive position, in order at length to hem in and capture the opposing armies on the coast, as they did finally at Yorktown. The open gate through the Hudson they strove to close early in the war by invasion of Canada. On the sea all they could do was to capture supplies and destroy commerce, and by the ravages of their privateers to inspire the enemy with respect. [Sidenote: Plans frustrated.] Neither party was able to carry out its plans. The British took all the principal seaports, but were able to hold none, except New York, to the end of the war. First Burgoyne and later Cornwallis made a determined attempt to penetrate far into the interior, and both were captured. On the other hand, the Americans could not shake off the main central army, and there was danger to the very last that the British would beat them in one pitched battle which would decide the war. [Sidenote: Campaign of 1776.] [Sidenote: Princeton and Trenton.]