Season 1 focuses on Congressman Frank Underwood and his wife Claire plotting to get him the vice presidency after he was denied the post of Secretary of State.
Season 2 has Vice President Frank and Second Lady Claire plotting to overthrow the presidency to take it for himself.
In season 3 then we learn that Frank's rise to the top was for the most part a Pyrrhic victory. Sure he's the president, but with a Republican Congress and a Democratic party that is plotting to run someone else in 2016.
But the biggest issue in Season 3 is the implosion of Team Underwood. Frank and Claire were always partners in crime (sometimes literally) but in Season 3 we find that while Frank has what he wants, Claire wants more than First Lady. She tries to become Ambassador to the United Nations and when she's rejected for having no experience, her husband gives her a "recess appointment," ie naming her the ambassador while Congress is on break. And almost immediately she runs into trouble with the Russians and resigns to basically become Frank's Eva Peron in Iowa.
What Francis can't understand all along is: why isn't First Lady enough for his wife? For two seasons (and 20 years before that) the White House was the brass ring. So why can't she be happy now that they're there?
This is one of the problems with human nature. We say we want something and then when we get it, we want more. For instance, up until a couple of years ago I would have said all I wanted was to get a book published. Then I got a book published and that simply wasn't enough. I didn't just want the book published; I wanted to actually sell some copies of it, which is where the "publisher" and I disagreed.
Pretty much every book or movie about rich people says this same thing. You can have all the money and stuff in the world and yet that doesn't make you happy because there's still something else you might want: friends, glory, power, or whatever. Like The Great Gatsby for instance. Gatsby had all the money, stuff, and fame you could want but he didn't have Daisy so he was just fucking miserable. And Daisy was married to some rich dude and she was just fucking miserable.
Hence what I'm saying: you can have the world and it's still not enough.