WASHINGTON—Foreign direct investment flows worldwide plunged last year due to the pandemic, which caused severe economic disruptions and forced companies to halt or delay investment decisions. United Nations data showed that the developed countries including the United States saw the biggest decline in investment flows. Global foreign direct investment (FDI) fell by 42 percent in 2020 to an estimated $859 billion, the lowest level since the 1990s, according to a new report by the United Nations Conference on Trade and Development (UNCTAD). The total investment flow last year was more than 30 percent below the trough seen after the 2008-2009 global financial crisis. Developed countries accounted for almost 80 percent of the decline, with fund flows plummeting 69 percent. The FDI flows to the United States halved last year, due to sharp declines in both greenfield investment (where an organization builds its operations from the ground up) and cross-border mergers …