CHAPTER III. Review (_continued_).--Triumph of the Democratic Party.--Impending Troubles with Mexico.--Position of Parties.--Struggle for the Equality of Free and Slave States.--Character of the Southern Leaders.--Their Efforts to control the Government.--Conservative Course of Secretaries Buchanan and Marcy.--Reluctant to engage in War with Mexico.--The Oregon Question, 54 deg. 40', or 49 deg..--Critical Relations with the British Government.--Treaty of 1846.--Character of the Adjustment.--Our Probable Loss by Unwise Policy of the Democratic Party. CHAPTER IV. Review (_continued_).--Relations with Mexico.--General Taylor marches his Army to the Rio Grande.--First Encounter with the Mexican Army.--Excitement in the United States.--Congress declares War against Mexico.--Ill Temper of the Whigs.--Defeat of the Democrats in the Congressional Elections of 1846.--Policy of Mr. Polk in Regard to Acquisition of Territory from Mexico.--Three- Million Bill.--The Famous Anti-slavery Proviso moved by David Wilmot.--John Quincy Adams.--His Public Service.--Robert C. Winthrop chosen Speaker.--Treaty of Guadalupe Hidalgo.--Presidential Election of 1848.--Effort of the Administration to make a Democratic Hero out of the Mexican War.--Thomas H. Benton for Lieutenant-General. --Bill defeated.--Nomination of General Taylor for the Presidency by the Whigs.--Nomination of General Cass by the Democratic Party. --Van Buren refuses to support him.--Democratic Bolt in New York. --Buffalo Convention and the Organization of the Free-soil Party. --Nomination of Van Buren and Charles Francis Adams.--Mr. Clay's Discontent.--Mr. Webster's Speech at Marshfield.--General Taylor elected.--The Barnburners of New York.--Character and Public Services of Mr. Van Buren.