The main theme of "Game of thrones" is politics and howbeit it has other theme as well and when you take a lot at everything the series revolved around you will noticed it's mainly politics and why do I say this?

We could see a possible hunt for the people trying to sit on the iron throne from Cersi Lannister to Danneryis Tagearyn the betrayal by Euron greyjoy and how he killed his brother to take over the salt throne is evidence of political corruption, the unruly desire for power and the insatiable urge to worship.

There is also themes like sorcery, magic, archaic believe in things like dragon, incest, prostitution acute nudity and the way of life of people who lived in the earliest centuries a very long time ago.

However the plot of the series centres on politics and the second will be political corruption and betrayal