Okay, this was an interesting 20 turns. After checking Diplomacy on my pre-turn, I saw that there was only 7 turns left on the ROP with the Ottomans, and 4 turns left on the lux. trade with the Celts. I decided that when the Celtic deal expires, not to renew it in preparation for war. Also, I was going to attack the Ottomans when the ROP expired

, so there was one less worry during the Persian-Celtic War. However 2 turns in, the Ottomans & Celts signed an MPP.
Early: Buildup of military forces to prosecute invasion of Celtic mainland. Moved transports and Destroyers in place to receive troops that were stationed outside lone French city on our continent.
Middle: Attack begun on Celts, Ottomans declare war on us as a result of their MPP. Capture last Ottoman city. Capture Burdigala (the nothernmost Celtic city), rush Airport, continue conquest of northern Celt.
Late: Took the northern half of the Celtic continent, moving troops in place to take two more cities, and the French break 3 trade agreements and attack us. They send
50 
Infantry, Guerillas, Medievel Infantry & Swordsman to stand next to Richborough (our southernmost Celtic city). They then send 45 Cavalry against our 3 Mech. Inf. and eventually take Richborough. They also capture and kill a few workers on our shared islands.
Richborough as it stands at the end of the turn:
Okay, for Nick, you get the fun task of probably completing our victory. I would think after we re-take Richborough and the rest of the Celtic lands, we should be at or close to a Domination victory (if this is enabled). There are still about 20-30 French units stationed in and around Richborough. I have bombed the road connections in the south where the Franco-Celtic border is, so it takes Cavalry 2 turns minimum to re-inforce the Richborough area. There are a bunch of transports and destroyers fortified off of our West coast that could be used to ferry troops over to the northern tip of France.
Also, next turn Synthetic Fibres will be researched, so you could upgrade the tanks to Mod. Armour. The Manhatten Project will be completed in the next turn or 2, & the Apollo & UN are ready in 3.
You will probably want to get a few troops over to the island where the last Ottomans city was located, as all we have left offensively up there is a lone Cavalry unit.
Our forces near Richborough are fairly depleted, so you will have to get re-inforcements there pretty quickly. I was having a lot of bad RNG rolls and losing a lot of units in the counter-attack on the French.
Here is the save:
N1 1860 AD