The Incredible Hulk

-GLITCH WARNING-
The game has glitched sometimes where if you don't destroy 25 assault groups overall they will stop appearing and you wont be able to continue with the story to get the 5 achievements.

You can check how many assault groups you have destroyed in the stats page.

Please take your time to destroy 25 assault groups before you destroy each base on phase one or continuing the story to much. Any mission passed after the Bi beast without 25 assault groups destroyed it might glitch out.

STEPS NEEDED TO TAKE TO TAKE DOWN A SECTOR
1.Each sector has 3 phases you must go through.
2.Each sector has a progress bar that needs to be filled up.
(you can check your progress bar in the missions page enclave)
3.You can fill up the sector by destroying the assault group that is attacking the city or replaying an earlier phase.
4. After the bar is full wait around the city and wait for it to talk about the enclave group has finished their weapon or w/e it says. and the waypoint will pop up for that city.
Keep doing steps 1 - 4 for each enclave sector.

the missions u need to take out the enclave's 4 sectors pop up randomly after u beat the game they dont pop up all at once so what i did was climb to the top of a roof leave the game unpaused and do something else for about 2 or 3 hours and when i came back to it they were all there

This solution applies for all 4 Enclave group achievements. In order to destroy a group you need to let the group evolve from Phase 1 to Phase 3. Each group controls one sector of the map. As the game progresses, you will see a purple dot on the map, one for each Enclave group. They will all be in Phase 1. You need to take each group to Phase 2. If you hit the back button, and then LEFT on the D-Pad, you can move to the ENCLAVE screen, which will allow you to see all Phases available for each group, along with the progress bar, which will be white and needs to turn red. Once the bar is red, then the group will be available to evolve into the next Phase. This will not happen automatically. In order to turn the bar red you can do the following:

Option 1: As you play on a particular sector, the group controlling the sector will eventually appear. You will see a red banner below saying something like "Warning. An Enclave group is active in this area". When this happens, you will see a few Enclave soldiers show up. You should stay away and let them do damage to the city. This will raise the bar to red.

Option 2: This other option is a lot easier and faster. You can replay a previous Phase (phase 1), over and over again. Each time you do, the bar will raise. These fights last 2-3 minutes.

Once the bar is full, you need to hang around the area controlled by the particular Enclave group you're trying to evolve. Get to Alert Level1. You will get the "Warning" message first. Just let them be, do something else, like going for collectibles, or hang out in some roof, but do not go into missions, mini-games, or anything that may interrupt them from damaging the city. If you choose to go hide on a roof, make sure the Alert level is still on 1, so you don't get any flying enemies. Go get a sandwich and come back. Eventually you will see a message saying that "the Enclave group has finished production of a special weapon". When this happens, a new purple dot will appear on the map for that Enclave group, and it will be Phase 2. Do this for all 4 groups.

For Phase 3, do the same. Keep playing Phase 1 until you raise the bar. Then go to the particular sector, get Alert 1, wait for Enclave to appear, hide, and wait for the 3rd dot (Phase) to appear on the map.

I did all this after completing all the missions, so you can do it that way too. When fighting the bosses for each one (they are all similar), do LT to lock on target, Jump and X, to hit it in the air. When he comes down, you can hold Y for charged hit, and you can also hit buildings to raise the bar and do an all out Thunderclap (with maximum rage bar). This will do a lot of damage.

I also got all the groups from Phase 1 to Phase 2, before moving any into Phase 3. It doesn't have to be that way, but I had no problems with it. You could get a group all the way to Phase 3 and eradicate it, before moving another group to Phase 2, I guess. But I didn't do it that way.

After beating the boss for each Sector, you will get an achievement. After beating all 4, you will get Para-Gone, another achievement. After you are done with all these, Save and Quit, come back into the game, get to Alert 1, and beat 1 enemy. This will unlock Veni, Vidi, Vici achievement.

Hope this helps.

This is for anyone who is having trouble filling the Enclave Progress Meters, especially for after beating the story:

Whenever an Enclave Assault Squad randomly shows up DO NOT IMMEDIATELY ATTACK AND KILL THEM.

Let them do whatever it is they're going to do and especially let them knock down buildings. The more damage they do, the more the meter fills.

You can watch from a high building, but they may knock it down so keep an eye on that. You don't want get too close to the group or they'll focus their attention on the Hulk. Just let them go about their business and stay above street whenever possible.

You will eventually have to destroy 25 of these groups for the Hulk Is Strongest One There Is! achievement, but they'll hang around and do damage pretty much indefinitely. If you raise your alarm level to 1 the Army will show up and the groups will attack each other. I do not know if their clashes fill the Enclave Progress meter, however, but I'd doubt it.

This can be done post game. I held off on all (4) sectors. Just revisit them via replay, get the red bar full. Hang out in the area afterwards causing havoc to threat level 1, let it clear out back to no threat level, keeping doing this until you get the Alert stating " Enclave group has finished production of a special weapon". Rinse and repeat for each sector, you'll eventually get the RED ALERT.

I followed Eric Filtro's solution and I can confirm it works.

If you can't get more Assault Groups to spawn and you still need 25 then you can just replay the base take over missions. Go to Map -> Push directional pad to the section "Enclave" -> Then select a base to take over. Each base will give you 2 Assault Groups.

Vulcan (East) just has 2 standard Assault Groups and is probably the easiest one to do.
Ceres (North West) will give you all Barbarians if you need extra.
Jupitor (North East) has shock people that stop your combos, kind of annoying.
Minerva (South) has mind control people so I wouldn't do this one.

I think Vulcan and Ceres are the easiest.