I don't understand "would be" in this quote. If you speak french, do you have any traduction?

The comitatus is the important men surrounding the leader, his entourage, but his military entourage, his armed men. Not just bodyguards, but members of a gang, I guess would be the closest simile.

'Would be' here is being used as a hypothetical suggestion - you could see this in the second conditional. If you were to ask me, this would be the closest simile.

Hope this helps

Bob

"Not just bodyguards, but members of a gang, I guess would be the closest simile."

This sentence is not very clear or precise English. Here it is, revised:

"They're not just bodygaurds. I guess that the closest simile would be that they are members of a gang." 

The speaker means "I think that the best comparison is that they are like members of a gang" or "They're not just body gaurds, they are more like members of a gang." 

<em>"Would be" </em>is just a hypothetical or weaker <em>"is" </em>in this case. The speaker is not committing to their stance.