Before Robert Baratheon overthrew King Aerys Targaryen the Seven Kingdoms were a relatively nice place to live. There was a balanced budget (a surplus actually), the peasants had food, and there was free trade between the kingdoms. Sure, Aerys burned alive a handful of his own constituents every year or so but what medieval ruler didn’t? Sure beat starting wars where hundreds of thousands died.
That’s pretty much what Baratheon and his lap dog Ned accomplished. Robert was in love with Ned’s sister Lyanna. But Lyanna and Rhaegar Targaryen (Aerys’ son) had a discreet thing going. Robert finds out, goes nuts. Starts spreading propaganda – backed by his in-law’s (the power hungry Lannisters) money and influence. Some of the kingdoms buy into it, old grudges re-surface, promises of land and money sway those on the fence and boom – you got yourself an insurgency – I mean “rebellion”.
Aerys is labeled “mad” and needs to be disposed of. Fast forward to Robert’s time on the throne – budget deficit (they actually have to borrow gold from the First Bank of Braavos, something Aerys would never have done), peasants rioting, and a continental war that has no end in sight.