Magna Carta was more a step in the direction of a parliamentary system rather than the pivotal point. It was notable in that it gave the council an important veto essentially, but in terms of its size, representation etc. it probably wasn't that great a break.
Political Interest wrote:1. Was the development of parliament unavoidable or could a strong king have potentially destroyed any forces which tried to create one?
Inevitably when you really need something from someone, you have to give them something (and that might very well be decision making powers) in return or they can withhold what you want. The monarchy wanted money, and parliament was in part representative of the people most likely to give the monarch that money. He couldn't really cut them out forever, and money can't always be gotten with force.
Political Interest wrote:2. Why did this system not develop elsewhere?
I'm guessing its a whole bunch of reasons, varying from country to country
- The monarch may have found some other way to making a deal without having to make as serious a compromise (devolution of power within the feudal structure, a better 'cut' of the tax pie etc.).
- The monarch might have been able to forge a sufficiently strong alliance (or system of dependence) that there was no serious challenge to their power. So instead of just the king vs. the barons, its the king and his barons and anyone who needs protection against the rest.
- For whatever reason you could have a structure (probably economic, but social or political considerations might be important too) where the centre is always stronger than any external challenger, so no one can force a compromise.
- Effective monarchy. If the monarch doesn't annoy people enough and does a good job, then there isn't a lot of incentive to hamstring them or replace them.