What exactly are the laws that have kept large companies small historically?

I have been hearing that laws have changed to make it clearer that large companies can be big without being held to anti-monopoly rules. But I don’t think anyone has actually commented on what exactly those rules were. <br><br>Was it the fact that you had to be a monopoly to be broken up? Because I don’t think Google or Apple or Facebook are monopolies. <br><br>Was it letting companies do „vertical“ combinations, like letting Google own search, add and YouTube? <br><br>Was it letting companies do cross-border acquisitions? <br><br>I think I heard someone say that companies used to have to demonstrate „consumer harm“ rather than just having a 30% market share.<br><br>But wouldn’t Amazon „harm“ small retailers? And wouldn’t Google or Facebook „harm“ smaller companies trying to grow?<br><br>I don’t really get how tech is somehow different from a previous era. Yes, maybe it’s easier to grow quickly through digital means, but we have several companies that are essentially monopolies now, and Amazon could potentially have a stranglehold on several sectors. Is anti-trust just broken?<br><br>I don’t really care if Google made search „better“. If it crushes MapQuest, Waze, DuckDuckGo, etc then how is that not the same as Standard Oil crushing smaller competitors? <br><br>If GM crushes Ford, then maybe that’s capitalism and it’s fine. But if GM crushes a car rental company, a taxi company, an Uber company and a parking garage company then how is that not anti-competitive? And how is it not a problem?<br><br>I don’t think we should go back in time, but I think anti-trust could be improved, and it’s not clear to me what exactly is broken.