Read the following text and answer the questions.

    For several years, President Roosevelt had been warning lawmakers and other Americans about the political forces in Japan, Germany, and Italy. Leaders in those countries supported nationalist movements and had already invaded or taken control of other areas.

    By 1941, more than 30 countries were involved in the conflict. Many Americans had wanted the U.S. to remain neutral. They regretted becoming involved in World War I. For years, they had taken steps to prevent another major international conflict. Lawmakers had even banned the U.S. government from selling or giving weapons to warring countries.

    But President Roosevelt believed World War II was different. He believed that Germany was the clear aggressor and needed to be stopped. So, in the 1930s, he received permission from Congress to provide weapons to the countries opposing Germany. After Germany took control of France, he received permission to give direct military aid to Britain.

    In addition, President Roosevelt began preparing the U.S. military for war. On December 7, 1941, Japanese forces bombed American ships at the U.S. Navy base in Pearl Harbor, Hawaii. More than 2,400 Americans died at Pearl Harbor, and more than 1,700 were wounded.

    The day after Pearl Harbor was attacked, Congress quickly approved President Roosevelt's request to declare war on Japan. Three days later, Germany and Italy declared war on the United States. American lawmakers responded in kind.

    The U.S., which had remained neutral for many years, was now completely involved in World War II.

"For years, they had taken steps to prevent another..." (paragraph 2)

what does the pronoun refer to?