"Our enemy is injured" - Our enemy is crippled
"Soon, they came," - please, not "they"

This is so extremly cliche

Also first you don't mention who it is and later give extreme details like "seven Dark Generals". Stick to one.
"Long ago, our people lived in an age of enlightenment. Through magic and technology, we had eliminated all poverty and disease. " - boring
"and was unable to contain the power he sought within." - irrelevant to the story. We don't care if the sorcerer succeed, the story is not about him. The sorcerer is only the trigger that brought doom to the world.
"We fought valiantly to defend our lands, but we were out matched." - yawn

Politician giving a speech.
"when a young warrior named Leo began to shift the tide in our favor. " - giving names out of sudden is strange. You didn't give the name of the sorcerer (much more important) or the name of the enemy.
"Through his leadership and incredible displays of power" - you want the reader dislike that warrior? No one values people who succeed by power. Warriors win by courage and sacrifice, not by power (at least in stories

).
"Leo, in his final move, " - he is not playing a game of chess, it is an epic battle. You don't make "moves" there.
"But he was not victorious, and lost his only son in the battle." A) he was not victorious and that's it B) he was victorious but the price was the life of his son.
"Our enemy is injured, but still very much alive. " - I though humans lost? Why suddenly it is "they" who are in trouble?
"The King has issued his final command from his death bed. Defeat the last of the Dark Generals, his lifetime Nemesis, at all cost." - it's like those kids playing generals and giving "genius" orders like "fire at them!". Come one, every single person in that realm knows these generals have to be defeated at all cost.
Overall, the story is OK, I have seen much worse

The biggest issue is that it is not epic. The war is basicly won (only last general remains, so 1/7th) when the real story (player's arrival) begins. No matter what he does, player will never, ever be able to do more epic act than the former king. The history will tell about the king who killed 6 generals, not about the player who cleaned up the battlefield by finishing off the last injured general.