Before there were the independent states of El Salvador, Guatemala, Honduras, and Nicaragua, there was the Federal Republic of Central America that also included Costa Rica and what is now the southern Mexican state of Chiapas. Panama was not a part of Central America but rather was a province of Colombia. When the US determined that the interoceanic canal should go through the Panama province, the Republic of Colombia refused, so the US incited a secessionist movement and recognized Panama as an independent state in November 1903.
