Which country invented paper?

China, traditionally credited to Cai Lun around AD 105, though archaeology has since found paper fragments a couple of centuries older - so he probably standardised and improved a process rather than inventing it. Either way it took a very long time to travel.

It reached the Islamic world in the eighth century, reportedly through Chinese papermakers captured at the Battle of Talas in 751, and paper mills followed in Baghdad, Damascus and Cairo. It did not arrive in Europe in quantity until the twelfth century, through Spain and Italy - so a technology invented in the first century took over a thousand years to cross Eurasia.

What it displaced explains its importance. Europe wrote on parchment, which is animal skin: a single large Bible could take the hides of two hundred sheep, which put an absolute ceiling on how many books could exist. Cheap paper removed that ceiling, and the printing press two centuries later would have been almost pointless without it - Gutenberg could set type as fast as he liked, but there would have been nothing affordable to print it on.