Simple Nabataea guide

Objective one: Take Adummatu
Turn 1 - Move the closest army towards Adummatu and muster new troops. Fast move your other army to follow it and give all the troops to the first army. This gives you almost a full stack by turn 2. Build buildings to get more food, happiness and money. You need to fix your happiness quickly.

Turn 2 and 3 - Build more troops with the second army. Move and take Adummatu.

Objective two: Take Yathrib
Turn 4 etc. - Once you have Adummatu move on Yathrib. You should have both in about 6 turns. You may need to fight off Saba, just enough to get a peace treaty or non aggression pact.

Objective three: Stability and money, and steal food
Make sure you have a non aggression pact with everyone you can get. You want one with Egypt, Seleucid and Saba as a priority. Make sure you have enough food and maximise your money. You will need it later. Get a Champion and dignitary asap. Put the champion with your best general to up his level asap. The job of the spy is to find enemy armies and steal food to weaken them. Upgrade their steal food with every promotion. The job of the dignitary is to advance in front of your armies to locate enemy armies. Make sure you have infantry tents in Adummatu or Yathrib. This is strategically important to build armies on your front line.

Why?
This is where your options are limited. Egypt blocks you to the north and are too powerful to take on early. Selucid blocks you too and is too powerful as well. Egypt will usually start to take out Selucid. Let them fight each other so they will usually ignore you. Also Saba is too hard for a frontal assault. They will run you around in circles between their three cites and you will never pin them down for the kill. Gerrha is too exposed and you will leave your centre open to attack by Saba. Never declare war if they have an ally. Instead, find someone they are at war with and offer to 'join war against'. You are then at war with them and the ally does not join.

How
Kush will usually declare war on you. This is good because you want them coming at you so you can wipe out their main army.

Step one: set an ambush at Charmuthas
You need a few units in your fleet and bring your full stack army and put it in ambush mode within reinforcement range of the city. Keep your second army at home near Yathrib and build to full stack to defend against Saba. Kush or Aksum will only see your little fleet as bait and attack. You will either wipe them as they attack your city or you can chase them down because they got too close. This is where your big treasury is comes in handy to quickly buy fleet mercenaries to smash them. Disband them to avoid upkeep.

Step two: Invade Ptolemais Theron and Meroe
If you kill the Kush full stack they sent at you immediately rush Theron city and take it. They will be mostly defenceless with the main army dead. Again, use Merc fleet units if required, you must win quickly. Keep the fleet in Theron and build a few units to hold off a Kush army out of Meroe that might flank you by rushing Theron as you attack Meroe with two armies. Build a second army in Theron and take Meroe. Take a spy or dignitary with you to see where their armies are.

Step three: Take Aksum
This should be easy with the two armies you have after killing Kush. Now you have secured your rear and gained valuable gold and land to grow food and make more money. Build temples to stabilise happiness.

Once you have killed Kush and Aksum rush over and attack Saba. The key weakness of Saba is Eudaemon. You need to take this to push Saba north and then east away from Yathrib and your other cites.

Setting up for the attack:
You probably have three armies and one fleet by now. One full stack near Yathrib, two over in Kush and a fleet near Ptolemais Theron. Try to build a fourth army south of Yathrib, even if it is a half stack. Use your spies to steal food and put Saba into starvation. Use you dignitaries to find and follow their armies around. Buy mercenaries when needed to make sure you win then disband.

Step 1: Move the forces in Kush to Eudaemon. Position the fleet ready to attack and land your two armies a little inland. Ignore the trespassing, you are going to attack them anyway. Get your Yathrib armies within range of Marib.

Step 2: Take Eudaemon and siege Marib on the same turn. This traps the Saba forces in Marib. As soon as you take Eudaemon rush Marib. If they break the siege of Marib withdraw and siege again next turn. You need to trap Saba in Marib to wipe them out. Don't let them get behind you and run for Yathrib.

Step 3: Take Marib. You should have enough forces by now. You really need to completely destroy any Saba army as you take Marib. If not chase them down asap.

Step 4: Go and take Maas-gat then Saba is dead. Rush your spies to steal food from Gerrha.

This is a transitional phase. You want to consolidate and get tier 2 units. Key is build enough food to max your income. Income and map position is everything! I had about 30 or 40 food and 3500 to 5000 income. Your number one general should be level 6 to 8 by now and can raise units at level 4 to 6. Replace him and raise him next turn in Adummatu and match him towards Gerrha as he builds troops. His job is just to build troops. Cycle your armies past him and fill them with better troops. Aim for 4 full stack tier 2 armies, depending on what you have available.
Try: 7x Desert pikeman, 6 x Axemen, 2 x Slingers, 4 x Javelins
Try: 6x Desert pikeman, 4 x Axemen, 2 x Slingers, 4 x Heavy archers, 3 x Arabian Cav

If they are vulnerable hit Gerrha, Charax hard and fast. If not, take some time to set up for the strike. Egypt will probably be winning against Selucid. Gerrha and Charax are a must have or you will get locked in. Selucia would be great if you can get it as well. You may have to go to war with Syria and others to get them and I ended up also taking Susa, Persepolis, Gor and Harmozia in the process.

Make peace and allies to seal your eastern border. Don't forget about Maas-Gat during this phase, it is very vulnerable to enemies out of Harmozia. If you lose it and get an enemy loose in your back yard, look out. This is where high income is crucial. Raise an instant army or fleet filled with mercenaries to save you cities and block enemies. Disband them when it is safe.

I see this as the only option to win the campaign. Wiping Egypt should be possible by turn 90 to 95. I got Egypt down from 15 to one or two cities way up north in about 5 turns and was ready to hold off Galatia at the same time. You should have 12 to 14 cities and an income of about 5000 by now.

This phase takes a lot of planning and patience. If you rush it and go too early you just awaken the beast (Egypt) and probably die. You need money, so research Quadag to get your cities up to level 3. Plan to grow enough food to support this and support later conquests, at least 40. Turn every port (almost) to a Trading Port, not food and not military to max your income. Upgrade the expensive ones that give you more money first, like gold and spice towns. Always have max dignitaries and spies to find their armies and champions to rank your units and Generals. Get your best General to build up 8 full stack tier 2 armies as fast as you can. If you have two good Generals, build in Petra as well. The same build is ok for this. You don't need tier 3 units, just what you are comfortable with, Camel archers, whatever.
7x Desert pikeman, 6 x Axemen, 2 x Slingers, 4 x Javelins
6x Desert pikeman, 4 x Axemen, 2 x Slingers, 4 x Heavy archers, 3 x Arabian Cav

Why?
In a military victory you must take Egypt. If you wait too long, they will far outpace you and block you out of the game. They will wipe Selucid and take all the cities up to Armenia and Tarsus.

How?
You need to do a coordinated, multi army, full court blitz on turn one of your attack.
Build 8 full stack, tier 2 armies and position them next to every Egyptian city you can and take all of them in one turn. I took 6 on turn 1 and followed up with another 4 on turn 2,3. Losing 10 cities in 2 or 3 turns is catastrophic and they will run out of money and food and can't support their armies for several turns. Follow up with steal food and they are toast.

South-west: position 2 armies just near each city
Turn 1 - Take Diospolis, Myos Hormos - one army for each with a fleet helping at Myos
Turn 2, 3, 4 - Rush Diospolis up to take Memphis then help with Alexandria. Rush Myos to take Alexandria

North-east: position 6 armies near all these cities
Turn 1 - Take Jerusalem, Palmyra, Hatra, Dura - one army for each with two positioned out of Selucid for Hatra and follow up to Edessa. One just near each of the other three. One in reserve (your best General) north of Adummantu.
Turn 2, 3, etc. - 2 Hatra armies move on Edessa then Antioch. Dura moves on Antioch. Palmyra or Jerusalem take Tyros or rush down to help with Alexandria.

Next turns: Wipe Egypt away in the south-west and make allies. Then you only have a one front war in the north. South, you should be able to take Alexandria, Paraitonion, Ammonium, Cryene. In the north go for Anitoch, Salamis, Tarsus, Tushpa, Samosata, Aramaosta, whatever it takes to destroy Egypt. Never make peace, kill them all.