Gerrymandering has existed for a long time. It is an act of disenfranchisement where politicians choose their voters rather than voters choosing their representatives. A few states created independent commissions to have neutrally drawn maps, but many draw them to maximize one party’s success, biasing elections against what people actually voted for.
Trump escalated gerrymandering by pushing Republicans in states they control to gerrymander shortly before an election, rather than after a census brings new data. This is Trump trying to win the midterm elections by way of changing lines on maps rather than by convincing people to vote for his party. Democrats retaliated by also gerrymandering before the mid-terms. For the midterms, Republicans are predicted to net 7 to 10 extra seats due to changing the maps, rather than convincing voters to vote for them.
Proportional representation may be a better way to elect representatives.