1) The rule of law is more important than brute force for social order
Much is made in Westeros about bloodlines, the right to rule, and the force needed to exercise that right. The death of King Robert Baratheon in the first season led to several seasons of jockeying by his brothers and other pretenders to the Iron Throne. The strength of a claim rested primarily on the strength of the army behind the claimant. Thus, Joffrey, the son of Robert's wife, Cersei, and her twin brother ascends the throne while Robert's younger brother Stannis has to figure out a way to bring his own family's forces under his command before attempting to take King's Landing. In the meantime, the presence of multiple claimants to the throne encourage Balon Greyjoy, a regional lord, to reassert his realm's independence from the Seven Kingdoms ruled by the Iron Throne.
Joffrey, meanwhile, is ill-prepared for power and moves immediately to abuse it, disregarding custom and any base standard of morals to literally do as he pleases as king. He beheads Ned Stark even after promising to pardon him, leading to war. He signs off on the murder of Ned's son, Robb, during a wedding. He also torments his subjects, is loathed by all, and eventually poisoned. Rather than making any effort to find the real killer, Joffrey's grandfather, the power behind the throne, instead uses his death to try to eliminate the dwarf son he detests. "The true moral of the story," Charli Carpenter wrote at Foreign Affairs, "is that when good rules are disregarded, disorder and ruin follows."