I weren't prepared for this war. For me this declaration was also surprising. Maybe we can provide our passwords and 2h files at the end of the game. Not necessarily for this issue but because of the much and often nice battles we had (and will have).
The thing with our NAP and arcane nexus may be discussible. As i said before for me is nexus a very aggressive spell (like utterdark) which has a heavy impact in all others gem using. This spell could be taken as a declaration of war to everyone. However thats my viewpoint but i admit that this may be debatable.
Well, i think you aren't defeated. You take over my best combat global and you have much armies with very good combinations of mages. Your huge arcane income give you a big advantage and good options to react. How many gems did you get from the nexus each turn?
Furthermore T'ien Ch'i decided to attack my backlands and take out most of my water provinces.
I appeal on all other player not to believe that ulm is defeated. Like a good diplomacy player he just play down his own strengths.