in the election of 1800, jefferson defeated adams. one of the most important things he did as president was to make the louisiana purchase from france, which made the united states twice as big. jefferson sent lewis and clark to map the louisiana purchase. jefferson also tried to stop trade with england and france so that the united states would not become involved in a war the two countries were fighting. fighting broke out between the united states and england in 1812 when james madison was president. this was called the war of 1812.