It was important for the frontiersmen to take the Lake Posts from the British; but it was even more important to wrest from the Spaniards the free navigation of the Mississippi. While the Lake Posts were held by the garrisons of a foreign power, the work of settling the northwestern territory was bound to go forward slowly and painfully; but while the navigation of the Mississippi was barred, even the settlements already founded could not attain to their proper prosperity and importance. Need of Free Navigation of the Mississippi. The lusty young commonwealths which were springing into life on the Ohio and its tributaries knew that commerce with the outside world was essential to their full and proper growth. The high, forest-clad ranges of the Appalachians restricted and hampered their mercantile relations with the older States, and therefore with the Europe which lay beyond; while the giant river offered itself as a huge trade artery to bring them close to all the outer world, if only they were allowed its free use. Navigable rivers are of great importance to a country's trade now; but a hundred years ago their importance was relatively far greater. Steam, railroads, electricity, have worked a revolution so stupendous, that we find it difficult to realize the facts of the life which our forefathers lived. The conditions of commerce have changed much more in the last hundred years than in the preceding two thousand. The Kentuckians and Tennesseans knew only the pack train, the wagon train, the river craft and the deep-sea ship; that is, they knew only such means of carrying on commerce as were known to Greek and Carthaginian, Roman and Persian, and the nations of medieval Europe. Beasts of draught and of burden, and oars and sails,--these, and these only,--were at the service of their merchants, as they had been at the service of all merchants from time immemorial. Where trade was thus limited the advantages conferred by water carriage, compared to land carriage, were incalculable. The Westerners were right in regarding as indispensable the free navigation of the Mississippi. They were right also in their determination ultimately to acquire the control of the whole river, from the source to the mouth. Desire to Seize the Spanish Lands.