He expressed his opposition to this method of obtaining new territory by resolution instead of treaty, and to acquisition of territory as foreign to the true spirit of the Republic, and as endangering the Constitution and the Union by increasing the already existing inequality of representation, and extending the area of slavery.

He dwelt on the inviolability of slavery in the States, and did not touch upon the evils of the system itself.
By the following spring the policy of Mr.Polk had culminated, intrigue had done its perfect work, hostilities had been brought on with Mexico, and in May Congress was invited to declare a war which the administration had taken care should already exist.

Mr.Webster was absent at this time, and did not vote on the declaration of war; and when he returned he confined himself to discussing the war measures, and to urging the cessation of hostilities, and the renewal of efforts to obtain peace.
The next session--that of the winter of 1846-47--was occupied, of course, almost entirely with the affairs of the war.

In these measures Mr.Webster took scarcely any part; but toward the close of the session, when the terms on which the war should be concluded were brought up, he again came forward.

February 1, 1847, Mr.Wilmot of Pennsylvania introduced the famous proviso, which bears his name, as an amendment to the bill appropriating three millions of dollars for extraordinary expenses.