The plane had engine problems and had to make a 'forced' landing in a field. [=the plane was forced to land in a field]
The pilot was 'forced to land' when one of the plane's engines caught fire.
He was 'forced' to resign from office. = He was 'forced' out of office.
(..) want to give me a for instance? First, you will hand over the Pink Panther. And second? - I will be forced to shoot you. - Who's forcing you? Open the door in the name of the law. Would you, please, sir, answer the door? (..)1975 The Return of the Pink Panther
(..) But you took it. Oh, I wish I had, truly. But I didn't, I swear it. Normally, I'm a man who detests violence, but in your case... I'm forced to make a most regrettable exception. Would it upset you too much to explain why? Under the pretense of trying to catch the thief, (..)1975 The Return of the Pink Panther