Translation:They are strong, and we are weak.
In this situation IAR is an adversative conjunction, it underlines the difference between strong and weak. There are situations were it is used as a copulative conjunction, like the conjunction și, but here it is not.
If that's the case, isn't it also possible that 'but' is a fine translation?
Multumesc! It seems like IAR may be like "while on the other hand..." in that it's a conjunction that illustrates a disparity of some sort...