Here is the full list of all 50 Command & Conquer: Red Alert 3 achievements worth 1,000 gamerscore.
You halted the Empire of the Rising Sun's cowardly and audacious ambush on the Soviet Union
You wrenched the launch facility at Krasna-45 from the clutches of the Empire of the Rising Sun
You completed every lesson in the tutorial in spite of all the bickering from the instructors
Complete Soviet mission 3 on any difficulty level
Complete Soviet mission 4 on any difficulty level
Complete Soviet mission 5 on any difficulty level
Complete Soviet mission 6 on any difficulty level
Complete Soviet mission 7 on any difficulty level
Complete Soviet mission 8 on any difficulty level
Complete Soviet mission 9 on any difficulty level
Complete Allies mission 1 on any difficulty level
Complete Allies mission 2 on any difficulty level
Complete Allies mission 3 on any difficulty level
Complete Allies mission 4 on any difficulty level
Complete Allies mission 5 on any difficulty level
Complete Allies mission 6 on any difficulty level
Complete Allies mission 7 on any difficulty level
Complete Allies mission 8 on any difficulty level
Complete Allies mission 9 on any difficulty level
Complete Empire of the Rising Sun mission 1 on any difficulty level
Complete Empire of the Rising Sun mission 2 on any difficulty level
Complete Empire of the Rising Sun mission 3 on any difficulty level
Complete Empire of the Rising Sun mission 4 on any difficulty level
Complete Empire of the Rising Sun mission 5 on any difficulty level
Complete Empire of the Rising Sun mission 6 on any difficulty level
Complete Empire of the Rising Sun mission 7 on any difficulty level
Complete Empire of the Rising Sun mission 8 on any difficulty level
Complete Empire of the Rising Sun mission 9 on any difficulty level
Complete all campaigns on medium or hard difficulty level
Complete all campaigns on hard difficulty level (also unlocks achievement for medium difficulty)
Complete all bonus objectives in the Soviet campaign
Complete all bonus objectives in the Allies campaign
Complete all bonus objectives in the Empire of the Rising Sun campaign
Complete 9 different online co-op campaign missions
Complete 18 different online co-op campaign missions
Complete 27 different online co-op campaign missions
Defeat a brutal-difficulty skirmish opponent on a 2-player map
Win battles on all original maps vs. skirmish opponents (medium-or-greater difficulty)
Win on 2-player maps vs. all 9 skirmish opponents (medium-or-greater difficulty)
Win on a 4-player map vs. a team of 3 skirmish opponents (medium-or-greater difficulty)
Leech 7 different enemy weapons using Hammer Tanks in a ranked online match or skirmish
Win a battle in less than 5 minutes vs. a skirmish opponent (medium-or-greater difficulty)
Destroy 30 enemy units with an ultimate weapon attack in a ranked online match or skirmish
Kill 25 enemy targets in 1 minute with a Commando in a ranked online match or skirmish
Crush 20 enemy units in a ranked online match or skirmish (medium-or-greater difficulty)
Cut down 15 enemy units with sword attacks in a ranked online match or skirmish
Arm 10 Multigunner IFVs with different weapons in a ranked online match or skirmish
Capture 6 structures in a ranked online match or skirmish (medium-or-greater difficulty)
Convert 5 enemy units with a single Spy bribe in a ranked online match or skirmish
Dismantle 4 enemy vehicles using the same Terror Drone in a ranked online match or skirmish