Party monopoly by decade (IMAGE) University of Arkansas Caption One-party monopolies were common during most of the 20th century. The most recent decade shows a dramatic uptick that favors Republicans. Credit Janine Parry Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.