Why does Jowy try to assassinate Riou instead of suggesting political union? If his goals is to end conflict by joining Jowston and the Highlands, and your best friend is leading the opposing side, wouldn't it be smarter to become allies rather than prolong the war and kill your buddy?
Which particular assassination attempt are you talking about? IIRC Jowy does try several times to get Riou to surrender to him. He wants an alliance all right, but with Highland in power, possibly because he sees himself as a Highlander.
Given the history between the two nations, I don't see how a Highland-Jowston political union could work. Although it was actually Jowston, through Mayor Darell of Muse, who started the war, they also have suffered so much at the hands of Highland, so do you really think they would just agree to make peace with Highland? No, because they don't even trust Highland's offers of peace anymore.
Basically Jowy had the firm belief that Highland and Jowston had too ugly of a history together for peace to ever last long. He didn't intend to kill Riou though, but he did intend to hold Riou hostage to force the City-State to surrender on Highland's terms.
Anyone care to explain why all endings except the Golden Ending is considered 'soul-crushingly depressing'?