Final answer:
Theodore Roosevelt improved the U.S. political and economic systems by enacting the Elkins Act to prevent unfair railroad practices and the Hepburn Act to regulate transportation rates, along with conserving vast amounts of federal land for public use.
Step-by-step explanation:
Theodore Roosevelt made significant contributions to improve the USA's political and economic systems during the Progressive Era. Two key initiatives he championed to confront big business and to support workers were the Elkins Act and the Hepburn Act. The Elkins Act, passed in 1903, targeted unfair railroad rebates, while the Hepburn Act of 1906 strengthened the Interstate Commerce Commission's authority to regulate railroad prices and extended its reach to other areas of interstate transportation, including oil pipelines. A hallmark of his presidency was also Roosevelt's commitment to the conservation of federal lands, resulting in the establishment of national parks, forests, monuments, and wildlife refuges across the country. This comprehensive approach to reform reflected Roosevelt's dynamic advocacy for the Progressive movement.