grammatical number - was and were in the form "X, along with the Y's, [was/were] Z"

Consider the sentence:

The aristocracy, as well as powerful merchant guilds, were viewed as restrictive to trade.

Should this be

The aristocracy, as well as powerful merchant guilds, was viewed as restrictive to trade.

How could it make sense in the latter case, since we are talking about a plurality of "merchant guilds"?