The New World Order (aka the NWO) conspiracy theory refers to claims of a hidden global power elite working to replace independent nation states with a single authoritarian world government. Proponents argue that this cabal which is often tied to wealthy bankers, politicians, and internationalists uses front groups, orchestrates or exploits crises, and advances collectivist or globalist policies as steps toward total control.
A few examples of supposed groups that people might suspect of trying to unify and control the world include the Illuminati, United Nations (a potential means to a unified world government), Federal Reserve System (for manipulating the monetary system which is another form of controlling the people), the World Trade Organization, World Health Organization, etc. Anything that gives additional wide spread policy creating and control over the populace basically.