How can we stop the creation of monsters like Amazon and Walmart in the future?

They have power over politicians and are capable of destroying small businesses. They can create a nexus point for trade and then call the shots.

We have let this happen but what can be done to stop it and prevent it on the future?

Any serious suggestions?

I thought about a growth tax to choke the business and prevent growth over a certain size. But I am not a business man. Also don’t want to become commie in the methodology.