As of Patch 5.0.14681.0, this still works. Tested out jayasme's method for Servants of the Land achievement for this achievement. Simply build gunpowder siege units and delete them. This will increase the counter for the achievement by 1. I used ribaulequins.
Set up your match 1 v 1 skirmish and set the AI to your team. This way you don't have to worry about attacks or anything else. Resources set to maximum. Make sure you are the French. Map doesn't particularly matter as long as you have room to build what you need. Remove all win conditions. Age IV.
Have your starting settlers start building houses and siege workshops. I typically would build ~10 siege workshops give or take. You can also build a blacksmith to research Military Academy to speed things up a bit.
Your limiting resource here is gold. So each session you will produce around 166 units. So it will take you roughly 6 games to build up to 1,000.
Once your workshops and houses are built, have your settlers gather gold. This will help squeeze in a few more units.
Simply que up the maximum amount of ribaulequins and wait. You'll have to periodically delete them to make room for more, but that is the point.
Once you run out of gold, surrender/restart and do the process over again.
I would suggest trying to work towards this while completing the French Mastery to save some time. Especially if your doing the island wonder method to complete the test of strengths. You have a lot of waiting and you can use the units to defend until the counter hits about 0.