Age of Empires II: Definitive Edition

First of all set your difficulty to standard to make your life easier.

In the start of the mission you need to choose where do you want to have your base. It doesn't really matter, the right side has a relic close to your base but that's the only difference that i found really.
First you want to get your eco going a bit and ignore water fights for some time. We need to clean the whole main island before we kill the purple docks. You have a lot of options what army to make, but i did champions and halberdiers, because it's the fastest way to kill buildings. Unique unit is also very powerful, but it's going to take some time to get the mass, since you cannot build additional castles. I added a few trebuchets behind because the byzantines castles are quite tanky. Blue will attack enemies from the other side aswell to help you. In the meantime purple will try with some landings by your base, but its not a big deal, if you want to be really safe you can make some towers or fortified churches.
When you cleaned the main island (grey, teal and green resigned) you can start to mass ships. Purple will have some galleons but just a few. Dromons are the best and fastest way to destroy buildings from water (unique tech is here useful aswell). You just need to destroy the docks from purple. There are five in the east, two in the south and two in west corner.

Achievement should pop after the mission is completed.