By the Declaration of the Right of Man, new ideas were put forward; everyone were born equal before the law which was contradict with the European powers who still practiced the hereditary hierarchy of status and it proclaimed of France ruled by its own people posed a strong opposition to the despotism rule of the European rulers. It was this sovereignty of the people, that had created a strong feeling of patriotism and it was further strengthened by the ‘levee en masse’ (the whole population of France was brought into permanent requisition for the defence of the country) in August 1793. Consequently, this led to the formation of a strong and disciplined revolutionary army during the Reign of Terror alarmed those European countries as it posed a serious threat to other European order of states( strong revolutionary army might invade their countries).
Practicing the Ancien Regime; those European countries were still very religious and had great respect for the Pope as he represented the head of the Catholic religion and held divine power for the kings to rule absolutely. Therefore, those European powers were angry when the Church privileges were removed such as lost of its incomes from the tithes, lands (were taken over by state), exemption from taxation, monopoly of education and control of poor relief and hospitals. All this was taken by those European powers as an insult to the Church which was always given a high position in the practiced of the Ancien regime. And the revolutionary assembly declared of the Civil Constitution of the Clergy in July 1790; removed the Pope power to appoint clergy as by this constitution; clergy was considered to be part of the government civil servants. This situation was further worsen in 1793 when the Hebertists adopted the system of dechristianization.
The revolutionary declared of the Edict of Fraternity in November 1792 in which they promised to help all people who rose against their rulers. This further encouraged the people of Europe to go against their rulers.
What those European rulers feared reached its height when King Louis XVI was guillotined on the 21 January 1793 with the set up of a new republican government and the radical actions of the revolutionary during the Reign of terror such as the September Massacres which might influence their own people to do the same thing.
European countries such as Britain, Holland, Russia, Spain and Italy reacted to all the above fears by forming a coalition against the revolutionary army. And as for Austria and Prussia; they declared the Declaration of Pillnitz (cause of Louis XVI was the cause of every monarch of France) and Manifesto (Duke of Brunswick declared that if the king was again humiliated similar to the incident of 20 June 1792 then he would carry out military execution and total subversion with the guilty rebels put to the death they deserved), trying to retain the old practiced of Ancien Regime throughout Europe, prevent the spread of the revolutionary principles and protect their countries from invasion of the strong revolutionary army.