Analysis of information sources in references of the Wikipedia article "History of group theory" in English language version.
Mit Vandermonde's im Jahre 1770 der Pariser Akademie vorgelegten Abhand- lung über die Auflösung der Gleichungen beginnt – so hat sich jüngst Herr Kronecker in einer Vorlesung geäussert – der neue Aufschwung der Algebra[With Vandermonde's treatise on the solution of equations presented to the Paris Academy in 1770 – as Kronecker recently said in a lecture – the new boom in algebra begins]
Cauchy states quite clearly that Vandermonde had priority over Lagrange for this remarkable idea which eventually led to the study of group theory.