For a century the French had held adverse possession; for a decade and a half the British, not the colonial authorities, had acted as their unchallenged heirs; to the Americans the country was as much a foreign land as was Canada.

It could only be acquired by force, and Clark's teeming brain and bold heart had long been busy in planning its conquest.

He knew that the French villages, the only settlements in the land, were the seats of the British power, the head-quarters whence their commanders stirred up, armed, and guided the hostile Indians.

If these settled French districts were conquered, and the British posts that guarded them captured, the whole territory would thereby be won for the Federal Republic, and added to the heritage of its citizens; while the problem of checking and subduing the northwestern Indians would be greatly simplified, because the source of much of both their power and hostility would be cut off at the springs.

The friendship of the French was invaluable, for they had more influence than any other people with the Indians.
Clark Sends Spies to the Illinois.
In 1777 Clark sent two young hunters as spies to the Illinois country and to the neighborhood of Vincennes, though neither to them nor to any one else did he breathe a hint of the plan that was in his mind.