Did you know that less then forty years after Elizabeth 1st reign had concluded, the English Civil War occured?
Did you also know this happened largely due to the aspirations of future Monarchs who were Scot imports because Elizabeth died without an Heir?
Did you know these Scots wanted to combine the Crowns of England and Scotland...and the English were not to impressed?
Did you also know that the parliamentary system was so corrupt (you'll notice it started right at the very end of Elizabeths Reign) by the time of the third conflict that England was under Martial Law for nearly a whole decade?
King Charles the First, son of James the First who took the throne after Elizabeth, wasnt very nice, and wasnt well liked. He married a Catholic for a start which is forbidden for the Monarchy since the reformation, and he wouldnt listen to the grieviences of his Government. When he tried to silence them they turned nasty, so he was forced out of London, and during the first war, basically pushed all the way up to Scotland
The Second conflict was the backlash from the Royalists which resulted in uprisings, and a partial invasion of Northern England by Scotland, who were acting on behalf of the English King....but it ended badly when the Military Forces controlled by the Parliament basically crushed both the scots and the rebellions. So then they caught and executed Charles the First above a banquetting building. The chopped his head off.
Now remember I said that Scotland was also a Monarchy? This is where it gets confusing. James the First of England, and James the Sixth of Scotland are infact the SAME person....and whilst the Stuart Lineage continued in England, the Scotish Crown as an independant thing seems to have sorta melted into the same thing after the Restoration of the Monarchy.
So Charles The First fleeing to Scotland and using Scots to invade northern England is mute since the whole realm was in theory run by Him. Charles the Second was also in Scotland, and it was his attempt to take the throne as the Heir of his recently executed Father. He failed, but he escaped to France of all places.
With both Charles The First and Charles The Second out of the way. A Five Year Republic occured. This Republic was disbanded by the very Military Leader that made it all happen, Oliver Cromwell, when the Government was found to be Corrupt. He then rulled as a Military Dictator for nearly the same length of time. When he died and his Son was found lacking by the Army, the Republic was reformed, and ran another two years before being dissolved by the Armed Forces, again because of political corruption, at which time they begged for the Kings Return
Now these Parliaments werent all quite the same. The Parliament that ran before the Conflict was called "The Long" The Parliament that was created for the Republic, disolved, and then re-established and then re-dissolved was called "The Rump" and the Parliament that was created at the Restoration was "The Convention"
Parliaments had names because they werent quite what they are now. They were a group of locals and a group of barons, and a group of Church Clergy, who was summoned to sit for certain amounts by the Monarch. They werent a permanent institution, so everytime the Parliament broke up, it was effectively being dissolved, who knew when the next parliament would be called, and whether the people on it would be the same or not. So the "Long" Parliament is litterally a referal to "The Parliament which sat for a long time" just like the one before it was "The Short" because it wasnt in session for very long.