Here is the full list of all 71 Napoleon: Total War achievements.
Capture 10 regions
Win 15 SP Campaign land battles
Capture a region in the Peninsular Campaign
Start any campaign, battle or historical battle
Win Egypt Campaign in easy
Win Europe Campaign in easy
Win Italian Campaign in easy
Win Egypt Campaign in medium within historic time
Win Europe Campaign in medium within historic time
Win Italian Campaign in medium within historic time
Win Egypt Campaign in hard
Win Europe Campaign in hard
Win Italian Campaign in hard
Assassinate 15 people
Have 6 allies simultaneously
Have a 100% approval rating
100000 soldiers die in battles with you, friend and foe
Gain 8000 per turn in trade revenue
Win ten SP Campaign naval battles
Conquer all of Europe
Have three generals with full skill level in one campaign
Have 10 protectorates at one time
Make all major nations like you (very friendly)
Declare war on all nations the first turn, never negotiate peace, and win the game
Cover 50,000 sea or land miles with your armies and fleets
Win 10 pistol duels
Win 10 sword duels
Play a historical land battle
Play the game for 30 hours total
Play the game for 50 hours total
Win Silver in 5 Historic Battles
Win Gold in all Historic Battles
Win a MP naval battle
Play a MP naval battle with every faction
Win a match with only first rates
Win 10 decisive victories
Win a match having spent half as many funds as your opponent
Win a match without any ships of the line
Play 100 multiplayer naval battes
Win 6 MP Naval Battles in a row
Board 5 ships in a single battle
Win 10 land battles
Play a MP land battle with every faction
Win 10 MP Land Battles in a row
Win a match without any infantry
Win 50MP Land Battles
Win a MP Italian Campaign as France
Win a MP Italian Campaign as Austria
Win a MP Egypt Campaign as France
Win Egypt Campaign as Ottomans
Play a MP Campaign
Win European MP Campaign as France
Win Europe Campaign as Russia
Win Europe Campaign as Austria
Win Europe Campaign as Prussia
Win Europe Campaign as England
Other player's faction is last to die
Win campaign having given enemy player 50000 gold
Play the game for 10 hours total
Win any campaign by auto-resolving battles
Win any campaign without a single autoresolve
Win a match against someone with double your skill rating
Win a battle using only Light Infantry and Artillery
Take other player's capital within 20 turns
Win a match against a player with double your skill rating
Win the Peninsular Campaign as France
Win the Peninsular Campaign as Spain
Win the Peninsular Campaign as Britain
As Britain, ensure that all regions in Spain are liberated back to Spanish control
As France, attain over 50% pro-French sentiment in 10 of your regions
Start the Peninsular Campaign in multiplayer