Why Hague is called The Hague?

Answer 1

I'm not sure about this, but I am certain it beats the last answer, which is: "Probably for the same reason Gambia is called The Gambia, whatever those reasons may be. We may never know."

Which is not very helpful, and perhaps the answer of an idiot.

My guess is that because the actual, technically correct name of the Hague, or Den Haag--which is 's-Gravenhage--is long and cumbersome to pronounce, for brevity's sake people nicknamed it Den Haag or the Hague. The nickname superseded the original to such an overwhelming extent that it became the de facto standard. The word "the" came to precede the name for the same reason it does many city nicknames: the windy city, the big apple, the crescent city, for a few examples.