bomb was thrown from a side alley. In the ensuing panic, police opened fire on the crowd and each other. Seven police officers and at least four workers were killed. Eight anarchists, directly and indirectly related to the organisers of the rally, were arrested and charged with the murder of the deceased officers. They became international political celebrities in the labour movement. Four of the men were executed and a fifth committed suicide before his execution. The incident became known as the Haymarket affair and was a setback for the movement and the struggle for the eight-hour day. In 1890 a second attempt, this time international in scope, to organise for the eight-hour day was made. It had the secondary purpose of memorialising those workers killed as a result of the Haymarket affair. Although it had initially been conceived as a one-off event, by the following year the commemoration of International Workers' Day on May Day had become firmly established as an international workers' holiday. Syndicalism saw its heights from 1894 to 1914, with roots reaching back to 19th century labour movements and the trade unionists of the First International. Subsequently, anarcho-syndicalism's main tenet that economic struggles come before political ones can be traced back to Pierre-Joseph Proudhon, and was the same issue that led to the schism of the First International. Anarcho-syndicalists advocated that labour syndicates should focus not only on the conditions and wages of workers but also on revolutionary objectives. The French Confédération Générale du Travail (General Confederation of Labour) was one of Europe's most prominent syndicalist organisations and, while rejecting illegalism, was heavily influenced by anarchism. As a grassroots organisation and lab for revolutionary ideas, its structure was exported to other like-minded European organisations. The organisation would later take a reformist path after 1914. In 1907, the International Anarchist Congress of Amsterdam gathered delegates from most European countries, the United States, Japan and Latin America. A central debate concerned the relation between anarchism and trade unionism. Errico Malatesta and Pierre Monatte strongly disagreed on this issue. Monatte thought that syndicalism was revolutionary and would create the conditions for a social revolution, while Malatesta did not consider syndicalism by itself sufficient. He thought the trade-union movement was reformist and even conservative, citing the phenomenon of professional union officials as essentially bourgeois and anti-worker. Malatesta warned that the syndicalist aims were of perpetuating syndicalism itself, whereas anarchists must