I can´t start the game while being offline

I am just about to come back to this beautiful game after a few years break, and I have just started up practising single player so that I eventually may want to start playing multiplayer-games again which I quite enjoyed before. However, I cannot start the game while being offline (no internet connection). This is not the way it used to be, I remember playing the game offline before. When I start the game being offline the game simply doesn´t launch. Is this just my computer, or am I doing anything wrong? It doesn´t matter if I go “offline-mode” on Steam, the game still doesn´t launch.

Thankful for any help! I really don´t like being online when I don´t need to since that just means I spend more time at the computer then intended, which I definitely don´t have enough time for…