It seems like every time we turn around, someone is getting booted out of England in this play. What's interesting is how the theme of exile is closely linked with patriotism. For Mowbray – and even more so for Henry Bolingbroke – being expelled from England makes them appreciate it more. Even Richard begins to appreciate England more when he's locked up in the slammer.
The thing is, this kind of patriotism wasn't a fully formed political concept in 1400s England, when the play is set. If you lived in England around that time, you probably thought of yourself as loyal either to a king or – perhaps later – to a religion. But Shakespeare wrote the play around 1595, when people were starting to think of themselves as loyal to their country. The play seems to anticipate the patriotism of Elizabethan England.
There are parallel versions of exile in the play: while Richard starts out by physically banishing Henry Bolingbroke and Mowbray, he ends up metaphorically exiled when he experiences an identity crisis.
The focus on England's soil, along with the emphasis on exile in the play, highlights the damage Richard did to the kingdom by leasing the land.