How did he do this ??

Hey,
I'm playing with higher level player now and I don't understand what's happening sometimes, if someone can explain me their trick it would be really cool.
So I was playing a World game, I was Algeria and the other player Germany, He got Italy first turn and some others countries and I had France so I protected paris and other cities to make a defense line so he wouldn't be able to attack paris directly next turn, well at least it was what I was thinking cause in spite of the defense line he conquered all France the second turn, how did he do ?

Also another weird thing is that before he attacked paris i had a group of some marines that I directed toward berlin but when he got paris they also disappeared

U may not have wall the city all the way

You said that you were making defense lines to prevent this. Were they in placed before he attacked you or did you move the troops and the next turn no defense lines were up and paris was his? As for the marines, you may ahve just lost the battle at berlin or if they were inside paris or a city they could have been turnblocked.