Fighting alongside the legendary Rorke, move down the street and ignore the enemies on the far side of the street; instead head around the corner and follow your team into a building that looks like it's about the collapse. Smart!
Proceed through the building and clear out the street behind it when the launcher's attacked. When the coast is clear, climb the ladder of the launcher (it's on the right side) and kill the soldier.
In the next street, defeat the soldiers on the right side first and hide behind the concrete blocks to take out the rest further ahead. Just when you were preparing to tour the city, the dam is destroyed. Follow your team into the alley to the right and enter the building. Keep following Rorke and go upstairs.
Kill the enemies straight ahead and continue. As you proceed, the roof quickly collapses and you're swept away with the current. When you're saved, follow Rorke and take out the soldier up ahead by staying underwater. Head upstairs and quickly move over the walkway connecting to the building across the street. Move around the corner and kill the two soldiers.
The desk in this room (where you just killed the two soldiers) contains a Rorke Intel. "Did you know that, Rorke?"
Go upstairs and clear the roof of enemies, then follow Rorke through the next building. As you drop down into the water, stay under and hide behind one of the boxes in the open area to avoid getting shot. From this position start taking out all enemy soldiers up ahead. Proceed to the boxes in the distance when the coast is clear and shoot any stragglers from there.
Climb the building, move over the straight path and drop down a building to be reunited with Ajax. Kill the soldiers in the building across the street and go inside. There are, naturally, more of them inside. Stay low to get a jump on the first few. Of course there are still more in the open area; defeat them all and proceed through the hall. Inside the chopper, kill the soldier and grab the gun when possible to shoot Almagro in the ass. After this, all you have to do is let go of Rorke (this is mandatory, otherwise you die and a 'Back To The Future' time loop starts to run infinitely, with you in it).