Alma 43:29

And now as Moroni knew the intention of the Lamanites, that it was their intention to destroy their brethren, or to subject them and bring them into bondage, that they might establish a kingdom unto themselves, over all the land;

Moroni knew what the Lamanites wanted to do. They wanted to destroy their relatives or make them slaves. They wanted to set up their own kingdom over all the land.

Moroni knew the Lamanites intended to destroy or enslave the Nephites so they could set up their own kingdom over the whole land.