duke o' york
It don't mean a thing....
The Vikings are most certainly not quaking in their boots. Now that we've paid them their protection money then they'll keep coming back for more and we'll have to ensure that they know their place as soon as possible. Not a great start to our diplomacy, but I suppose this was what the people instructed our Queen to do so well done to her!
Damned democracy! 
I am going to presume that we are not going to concern ourselves with our reputation too much in this game so this peace treaty won't set us back too far. Once our forces arrive in striking distance of the AI though, can I suggest that we demand tribute from them so that they declare war on us and our rep is intact.
[/regular citizen]
Settlers stand a decent chance against horsemen; I probably would not have paid. But that's water under the bridge. Plan for Dip/Chariot/Archer to head North is great. Personally, I would not expend any resources beyond that worrying about the Viks at the moment (other than ensuring all our Northern settlers and newly founded cities have adequete protection. As long as all cities are otherwise well defended (at least a Phalanx) then we need CARAVANS and lots of them for trade and wonder building!! (As soon as we actually discover trade in a couple turns, anyway). While our Northern expedition clears our continent of the odorous Vikings, our empire needs to focus on trade (=science), and I'm not just saying that as the Science Advisor. Let's not get drawn into a resource-draining war unnecessarily with the Vikings. Clear our continent with the minimum force possible, send settlers/defenders North to found cities so it won't happen again, but let the rest of our empire focus on trade/science.
