Age of Empires II: Definitive Edition

The achievement pops if you have to have 100 or more points at any time during the game, so you dont have to maintain it and it doesn't matter if you go below 100 in the future.

You start with 20 and but you're slowly losing piety points over time. Therefore its good to collect them early and then focus on defeating the enemies. Your ally mostly deals with incoming forces, so you dont have to spend resources on military immediately. Here's how to collect 100 fast:

-->Researching all 5 available university technologies gives you 25 easy points.
-->There are 4 easy to find monestaries for another 20 points:
1. north western island: west of your ally
2. south eastern island: west of your ally
3. center island: slightly left of center
4. northern island: in the east
-->In front of 1. and 2. there are relics for another 20 points. Another relic is below your northern base
-->Builing a wonder gives you another easy 20 points, The enemy wont attack you for building it, but it also doesnt win you the game.
-->Finally, converting 20 units: red continuously send ships to your ally in the west. if you send 5-6 monks there, you can easily convert 20 ships.