So, we've all seen Radiant vs Mistborn and that makes since considering that they are the two most popular, but I'd like to see some other types of interactions so here's the first in the series.
Let's start with a few basic assumptions.
Both Worlds are completly united
Both sides are bloodlusted, i.e. no peace no negotiations, but this does not exclude long term planning
Shards do not intervine, not that Sel's can at this point, but I thought I'd mention it.
I think the conflict starts obviously enough, Radiant and Fabrial shock troops annialate everything in their path but are sloowed to a standstill when they encounter other magic, in places like Arelon and Fjordell, Dakor monks are willing to sacrafice enough of themselfes to create warriors capable of fighting Radiants and cause a standstill, Elantrins are capable of weilding enough power at a time to at least cause problems, depending on how far they have advanced, but given the connection orb in SH I think they can hanndle themselves, however the Rose Empire and Mai pon get completly steamrolled.
After this a breif stalemate occures and an arms race ensuses with both side trying to overcome the other, if Arelon can build a larger Elantris effectivly turning all of Arelon into a giant aon Rao they might obtain enough power to drive off the invaders.
but what do you think?