The Holy Alliance was a coalition of Russia, Austria and Prussia created in 1815 at the behest of Tsar Alexander I of Russia, ostensibly to uphold Christianity in European political life but in practice as a bastion against revolution.
The Alliance is ususally associated with the Quadruple and Quintuple Alliances, which included Britain and (from 1818) France with the aim of upholding the European peace settlement concluded at the Congress of Vienna.
The Alliance is conventionally taken to have become defunct with the Alexander's death in 1825.