Re: Robb S/Daenerys T
Not long. Only long enough for your ancestor Aegon to conquer most of the Seven Kingdoms, before he finally reached the North. My ancestor Torrhen Stark marched to meet him in battle, but bent the knee when he saw the might of Aegon's forces - not to mention his dragons.
He was a wise man, but I've long believed that Aegon would have been wiser to see the strength in an alliance, rather than mere subjugation.