The Siege started badly for House Strong when Stephon Strong was killed in the opening moments by his own gaurd. Following this murder the supposed mercenary army of House Seaworth - which was in fact simply soilders from the Iron Islands - landed in a fleet inside the port, and attempted to take control of the city. The siege ultimately failed after Kyle Strong along with a brigade of his men held the road to the Keep for long enough for reinforcements under Robert Strong to arrive.
The Siege has split the once completely dominated House Strong Harrenhall into a desperate battle for control between House Strong and House Seaworth.
When looking at the background of the siege of Harrenhall it is important to look at the elements within the city of Harrenhall that caused the siege, and on top of this why the Iron Islands decided to become invovled.
Main Article : Harrenhall
See Also : House Strong
The city of Harrenhall from its earliest days as a true city had been controlled by House Strong, who had an iron grip on power in the city. To control the city the leadership of House Strong placed their banner houses in positions of power that led them to control something of their own, but at the same time still be devided from eachother and thus no threat to House Strong.
See Also : House Seaworth
House Seaworth had been for much of their history the second or at the worst third strongest house in Harrenhall behind only House Strong, and at times House Gronn. This position was cherished by the leadership of House Seaworth for much of their history, and they were rewarded with control over the port of Harrenhall which was hugely important to the cities power.
Main Article : Iron Islands
The Iron Islands was a very expansionist Kingdom and they were always interested in controlling Harrenhall, as from Harrenhall they could attempt to control the entire Dolish Penensila. At first they attempted diplomacy as the city itself was very strong and they didn't want to attack the city for fear of heavy losses. Their diplomacy was rebuffed by House Strong who wanted to control Harrenhall alone.
With diplomacy over they had attempted to gain control of the banner houses of House Strong but were rebuffed in their attempts at every turn by a people who were very ideologically opposed to the Iron Islands.
The growing discontent of House Seaworth reached its pinacle and the basic end of the line, when they attempted to gain influence in the small House Jare, and when this was discovered Robert Strong had Halten Seaworth put in jail as punishment. With this imprisonment the leadership of House Seaworth came to the conclusion that House Strong were tyrants that they should take the mantle of power in Harrenhall from. They decided to do this by reopening the channels that had existed with the Iron Islands before they had cut ties with such rebellious thoughts.