Nice Muli :) unfortunately I cannot do this on app because the limit to a custom scenario darting armies is 100 and many maps have more than 100 territories. If someone could make me a valid template I would be really happy.
Bridges of Konigsberg is an example of a graph with no Eulerian path. In general, it's easy to determine if a graph has an Eulerian path - a vertex of odd degree must be the beginning or end of an Eulerian path. What Benjamin is asking about is Hamiltonian path; in general, this is a much harder problem.
Edit: of course, Warlight maps are typically planar, and only include a few small cuts, so probably most Warlight maps have Hamiltonian paths, and probably they're not too hard to find. Edit2: replaced one "cycle", which occurred only in the edit and which was a typo, with "path".
Small (nitpicky :p ) correction: you don't need a Hamiltonian Cycle (where the start and end vertex are the same), a Hamiltonian Path (which is allowed to have distinct start and end vertices) suffices.
The most probable cause for a WL map to not have a path like that, is when it has three (or more) "dead ends", territories with only a single neighbour. Maps of subway systems are pretty much guaranteed to not allow this kind of scenario; "geographical" maps are very likely to work though (even a map of, for example, Croatia should probably work; while Dubrovnik is likely a dead end, maps can have up to two dead ends and still work).