Most demons have territories. For example there was the "prince of Grecia" and the "prince of persia". (Daniel 10:20) And in Mark 5:9-10 we see the demons did not want to be cast out of the country they were in.
However, with satan himself; it is different. He is prince of this world. (John 14:30) The whole world is his territory.
So, Satan is often on the move. He comes to steal, kill and destroy.
And the Lord said unto Satan, Whence comest thou? Then Satan answered the Lord, and said, From going to and fro in the earth, and from walking up and down in it.
Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour: