@ds61514 , he waited to long to go on the offensive . By the time he used to spawn 3 cities , he should have already conquered 1 ai and in a good position with the second .
Horsemen are powerful no doubt about it, but you kinda reach a dead end after 2 or so AI .
By going archery and making warrior +2 archers in the capital, then beelining iron working/mathematics . You can use the initial forces to conquer 1 ai ,maybe 2, upgrade those warriors to swordman and conquer 1 more ai , and by the next one you will have catapults .
To note, that the warriors/swordmen are to be used only to defend fortified position in forest/hills until he smashes his army into them , having the archers/catapults for support for cities .
You need to be way more aggressive . Raze his cities and keep capitals, when you are alone on the continent you can stop to tech, if its pangea never stop, you should be in a constant state of war, even if your not making to much of a progress towards the last 1-2 ai, you will keep his production busy making troops instead of anything else while you catch up and/or gain military superiority either by numbers or careful tech to better units .
This strategy is best played as Japan, since it makes your tanking troops way more effective always fighting at full strength regardless of their hp .
The later you start warmongering the sooner you will meet the "wall" where the further AI will have a better army even if just from numbers, and you need to gain tech advantage .
P.S. i noticed your other 2 immortal game videos, where is the rest of them ? you have only the first part of each . Did you give up ? .