Here is the full list of all 40 Defend The Highlands achievements.
Kill 500 Posh Englishmen
Get 500 kills with Robin Hood
Kill 500 Ancient Briton Warriors
Kill 500 Leprechauns
Recruit 1,000 Scotsmen in total
Have 5,000 porridge at once
Hit 5 enemies with a single artillery strike or haggis
Have 2,000 gold at once
Fully upgrade all stats on a single unit
Kill 1,000 enemies with porridge bowls
Kill 500 enemies in melee
Kill 500 Irish Potato Farmers
Kill 500 Welsh Rugby Players
Kill 500 English Cricket Players
Get 500 kills with Alfredo
Kill 1,000 enemies
Complete a skirmish match on easy
Fully upgrade a stat
Recruit 100 Scotsmen in total
Kill 100 enemies
Kill 10,000 enemies
Kill 1,000 enemies with porridge cannons
Kill 500 enemies with whisky vomit
Kill 1,000 enemies with golf balls
Kill 1,000 enemies with haggis catapults
Kill 250 enemies with bagpipe artillery
Kill 1,000 enemies with turnip turrets
Kill 500 enemies with cheese wheels
Get 500 kills with William Wallace
Get 500 kills with Queen Boadicea
Kill 500 Welsh Sheep Riders
Kill 500 Beefeaters
Complete a skirmish match on medium
Complete a skirmish match on hard
Complete a skirmish match on impossible
Complete a skirmish match without heroes
Complete a skirmish match without towers
Kill 15 enemies with Nessy in a single match
Defeat a level 6 enemy on level 1 in skirmish mode
Have 50 Scotsmen at once