So if i decide to steal a tech from a city, and the opponent has an army there, do i have to fight the army or can I sac my unit and get a tech ?

 You can't station armies or scouts in your own cities. You can only move armies (or scouts in the case of russia) onto opposing cities.

edit. Nevermind , awesome.

EvilAmarant7x said:

Actually you can station armies or scouts in your own cities to be protected by the city (via battle points) or by adding+3 to the defense.  Basically if you have a city and and an army stationed there, the total Battle stack is 6 (three from the army + three from the city).  The result is a tough city to crack.  The downside is that the defender is stuck there and not on the offensive.

Maarek said:

Nope sorry. From the Rules in the Movement section under Friendly and Enemy Cities:

A player may move their figure through their own city centers, but they may not end any figure's movement in their city center.

And you build new figures in a city outskirts AND the rules also state if their are friendly figures in the same space as a scout when it builds a city they are moved to the city outskirts.

So there's really no way to get a figure into a city.