The most obvious answer would be that "Moscow'd" here refers to the burning of Moscow following the invasion of Napoleon's Grand Armee. The burning of Moscow has been attributed to both the Russians and the French. Perhaps implying that if you keep massacring people you will end up burning the whole country down.

The other plausible explanation would be saying "Keep repressing the people and you'd end up like Moscow." This would be not referring to the actual city, but instead to the governmental system of the Russian Empire. The Russian Empire was an autocracy with repression and suppression of the people including serfdom at the time of this writing. Being "Moscow'd" would then mean to become an example of a complete dictatorship without liberty. This likely is a more plausible explanation of the sentence. The author could have ignored that the capital of the Russian Empire at the time was St. Petersburg because of complicated sentence of Peterloo plus Petersburg. Also, Moscow was still seen as the cultural capital of the Russian Empire and Tsardom even if the governmental capital was in St. Petersburg.