惑星連合（Coalition of Planets）は2155年に設立された、アルファ宇宙域及びベータ宇宙域のいくつかの政府によって設立された緩やかな惑星間同盟であった。これはその6年後に設立された惑星連邦の前身となる歴史の第一歩であった。連合結成の為の最初の会談は地球のサンフランシスコで行われ、地球連合、ヴァルカン、アンドリア帝国、ライジェル、デノビュラ、コリダン及びテラーの各代表が参加した。（ENT:テラ・プライム・前編）
It is possible that the Coalition of Planets is the interstellar equivalent of the League of Nations, which was founded a year after World War I had ended and was dissolved a year after World War II had ended. The League is regarded as a predecessor of the United Nations which was founded eight days before the League was officially dissolved. The Coalition of Planets was probably dissolved in a way similar to this after the Earth-Romulan War ended. Its role in that conflict is unknown.
It could also be interpreted as similar to the United States Articles of Confederation, which was eventually superseded by the United States Constitution. While the Articles "created" the first American government (whereas the Declaration of Independence and Treaty of Paris actually created the US as a legal body), the Constitution made it a viable system of government. You could be seeing the "birth" of the Federation, while the Federation Charter has yet to be written.
Some fans have taken the charter signing ceremony seen in "These Are The Voyages..." to be the signing of the Coalition of Planets' charter or the charter for some other alliance other than the UFP Charter; this is based upon Troi's line in which she remarks that one wishes to tell the holographic participants that "this alliance will give birth to the Federation." While that is a legitimate interpretation, it is not necessarily canonical, as the line itself is ambiguous and could easily refer to the present state of the Federation as its own nation rather than an alliance. Although, other fans have pointed to the exact same scene was observed in "Zero Hour", in which they believe that the scene itself explicitly identifies the signing of the Federation Charter. However, there is insufficient canonical evidence for either interpretation. Daniels expressly states to Captain Archer: "Do you remember, I told you about the Federation... you are going to be an integral part of forming that Federation. You're down there right now, with Vulcans, Andorians and Tellerites getting ready to sign the Charter. The membership is going to grow, dozens, eventually hundreds of species, a United Federation of Planets." It is strongly inferred by the mention of 'that Federation' and 'the Charter' and the date of 2161 that the scene is the signing of the Federation charter, but it could simply be the signing of another document which led to the final Federation Charter. This conclusion would be consistent with both Daniels' statements and Counselor Troi's statements, "this alliance will give birth to the Federation." Clearly and logically the signing of any pre-Federation Charter alliances, treaties, such as a document officially establishing a post Earth-Romulan War Coalition would be an integral step in the birth of the Federation and Archer's presence at any stage in the development of the Federation would be important. Also, the fact that the writers of both episodes left the scene's purpose vague leaves substantial doubt as to the exactly what document was being signed at the assembly.
It is interesting to note that Coridan was apparently on track to become a member of the Coalition of Planets, yet "Journey to Babel" and "Sarek" clearly establish that Coridan did not join the Federation until well over a century later. Also, Denobula-Triaxa may have joined the Coalition, but may have refused to sign the Federation Charter and may never have joined the Federation at all.