Land grab is when a player builds on a certain area of land with the purpose to build their base, or, what it is usually referred to, with the player's intention to 'steal' land so that it cannot be built on my their opponent(s). Unlike painting, this is not considered an unfair or cheap tactic, as it is a matter of skill and timing to steal all the land, and the large quantity of available land already creates a fair game.
Land grabbing is a very powerful strategy and should not be underestimated. Its greatest power and importance is shown in games where two opponents start very close to each other, or in 1v1 games.
Consider if your enemy has taken all the land for you to build on, but has not painted you. This leaves you room for you to only build around your Town Centres, while your enemy can freely build anywhere on the map.
How to deal with it
There is not one single strategy which can re-steal land as there are too many different types of scenarios. Common approaches to dealing with land grab are:
1. Building a tower which will destroy the enemy's unbuilt buildings
2. Building barracks close to the Town Centres so that a legion will destroy the unbuilts through manual controlling.
3. **Sneaking (backdooring) to the back of where the enemy's base would be.