Your text spent three chapters interrupting the flow of the narrative. Notice that it is now picking up the story where it left off in chapters 13 and 14 after our sidetrips into economics, culture, and the slave system. Make sure you review what was going on with the British, with Texas, and with Oregon in previous chapters to help you understand chapter 17. The pages you will want to review are: pp 265-267 and pp. 295-298. Make sure you note treaties and agreements from that time period.
Also, you might want to brush up on what exactly the Whig party held as its core beliefs. Pages 290-292 and 298-301 will help explain some of the politics in chapter 17. For some reason, the book suddenly left off its discussion of the Whigs and William Henry Harrison at the end of chapter 13 and now picks it up again at pages 396-97.