Some argue (e.g. Chang, 2002) that it was in America that he gathered from a study of Alexander Hamilton's work the inspiration which made him an economist of his pronounced "National System" views which found realization in Henry Clay's American System. Others deny this (Daastøl, 2011), since he argued for a German customs union already in 1819, when he established the first German union for industry and trade. List's ideas on protectionism predate his American sojourn, and were influenced by liberal protectionists such as Adolphe Thiers. The main theoretical reference approvingly cited by List in his 1827 pamphlet "Outlines of American Political Economy", in which he defended the doctrine of pragmatic protection and free trade, was Jean-Antoine Chaptal’s "De l’industrie française" (1819). The discovery of coal on some land which he had acquired made him financially independent.