US Army with (either) an AT-AT, Liberty Prime or Gipsy Danger vs The Grand Army of the Republic (limited vehicles)

If you don't want to read the wall of text, there is a shortened TLDR below. However, if you need more details, I'd suggest first reading the unabridged text for more details before commenting.

The US is continuing fighting in the Middle East, advancing on a rapidly declining Daesh (ISIS/ISIL) force. Extremist propaganda has failed, all remaining troops are hiding in a fortress with US embassy hostages, on the other side of a sand dune covered in an array of land mines. As the US formulates a strategy, a rift opens up in the ISIS stronghold for Commander Cody from the Clone Army to carefully walk through. He speaks to the men and learns (through albeit biased viewpoints) that the United States is "restricting religious freedoms" and "on the verge of destroying the planet", in addition to being controlled by groups of large trade alliances (suspected by Cody to be the Trade Federation).

In addition to giving Cody and his scouting team some info about the planet's resources and climate (potentially being a good ally and source of resources for the Republic) Cody agrees to help the "freedom fighters" defeat the "trade federation funded Empire". The Republic devotes all ground forces to this endeavour, but due to the size of the rift cannot bring vehicles bigger than speeder bikes and IFT-X vehicles.

A similar rift opens in the American camp discussing tactics for the mission at hand. A mysterious man enters and convinces the personnel to stand down, as he explains the capabilities of ISIS's new allies, as well as how many (around 1.2 million) troops and the capabilities of the speeder bikes and IFT X vehicles they are going to bring through. He offers to help level the playing field slightly, but suggests the outcome is dependant on how they use the gift. He gives them three options, and decides to lockdown all nukes on the planet to avoid planetary devastation. The US can persuade other countries to assist, but only the US can deploy vehicles in this fight.

Fight takes place in the Arabian desert, upon deployment Clones deactivate the mines to advance. The armies are given two months prep. Clones can only have 20 IFT X + 40 SB active at a time (to prevent IFT X/Speeder stomp. The three options are listed below.

Round One: The US opts for the gift of an AT-AT walker, freshly made and fully stocked. They can choose to try and reverse engineer some of the tech in the two months prep they have, or they can deploy it in battle as is.

Round Two: The US opts for the gift of Liberty Prime, "borrowed" from the Brotherhood of Steel (Fallout 4) after he has been restored to full working order. Fully stocked with nukes, optical blast fully operational, Prime can be deployed as is or they can attempt to dismantle and reverse engineer parts of him.

Round Three: The US opts for the gift of Gipsy Danger from Pacific Rim. Fully prepared for combat, delivered with a program that trains any two American soldiers to pilot the Jaeger in a single day. However, the Clones are given an AT-TE in addition to their regular vehicles.

Bonus Round: The US chooses all three, which is granted due to the chaos possessing all three would possess. The Clones have access to all (non-space, so no orbital bombardment) Republic vehicles, but are limited to 40 SB, 20 IFT X and 30 aerial vehicles (including Starfighters, Gunships, Personnel Carriers) at a time on the battlefield.

TLDR: Prompt) Republic Army sides with ISIS through biased propaganda. Republic has entire infantry available, but 40 Speeder Bikes and 20 IFT-X tanks at once due to the odd rift they entered through. No other vehicles for them. America can persuade other countries to send infantry to assist, but no non-US vehicles allowed. America given one of three Sci-Fi assets to assist their effort. Two months prep for both sides after Clone+ISIS first contact/America given the asset of their choice. No nukes or bombing the camp, as they have Embassy hostages in the opposition base.

Round 1) US Army + Fully functional AT-AT. Both sides morale-lusted, willing to fight to the last man. Victory achieved by capturing the enemy stronghold, or elimination of the enemy force.

Round 2) US Army + Liberty Prime (Fallout 4). Same as before.

Round 3) US Army + Gipsy Danger (Pacific Rim). Same as before. Republic Army now has one AT-TE walker available.

Bonus: US Army gets all three assets, Republic Army gets access to all (non-space) vehicles, albeit only 40 speeders/20 tanks/30 aerial vehicles at a time.