Final answer:
The assertion that Buchanan's actions held the Democratic Party together is false; his attempts to appease both sides of the slavery debate failed to prevent the party's split, which contributed to the onset of the Civil War.
Step-by-step explanation:
The statement that Buchanan's actions while in office helped to hold the Democratic Party together is false. James Buchanan attempted to please both the pro-slavery and anti-slavery factions within the Democratic Party by not taking a hard stand on the issue of slavery. This led to further division, especially since his indecisiveness failed to address the escalating tensions that led to the Civil War. Southern Democrats ended up splintering, contributing to the party's inability to hold together as a single unified force.
Regarding the other historical statements provided, William Henry Harrison's victory over Martin Van Buren in the election of 1840 was a victory for the Whig Party, not the Democratic Party. Southern redeemers did not hope to preserve Republican rule; they were actually opposed to it and sought to restore Democratic control. President George W. Bush's foreign policy was not characterized by liberal internationalism; instead, his policies were more closely aligned with neoconservative principles. Lastly, economic sanctions employed by Jefferson known as the Embargo Act indeed failed to solve tensions with Britain and France. In the election of 1860, the split between Northern and Southern Democrats and the Constitutional Union Party's split of the vote were among the factors that contributed to Lincoln's victory.