The treaty is problematic for a variety of reasons ranging from the substantive to the procedural. On substance, the treaty is designed to regulate arms importers and exporters, which the United States already does. The treaty, however, does not properly regulate foreign countries, leaving the United States on the hook while leaving actual wrongdoers alone. Meanwhile, signatories are supposed to keep information on “end users” of arms imported into their country and to give that information to the supplying country. In other words, it makes it more difficult for American citizens to import arms, and guarantees the solid chance that foreign governments have information about domestic gunowners.
Procedurally, the United States originally insisted that the treaty go through consensus decision-making, meaning that everyone sign on. But when a conference to do so failed, the US decided that the treaty did not need to apply to all countries. Countries abstaining from the vote include China, Russia, India, and Egypt.