Necessity compelled him to work with the clergy and people rather than the gentry; hence it was that the Riksdag of the Estates assumed under his regency government a power and an importance which it had never possessed before. In 1595, the Riksdag of Söderköping elected Charles regent, and his attempt to force Klas Flemming, governor of Österland (Finland of the day), to submit to his authority, rather than to that of the king, provoked a civil war. Charles sought to increase his power and the king attempted to manage the situation by diplomacy over several years, until fed up, Sigismund got permission from the Commonwealth's legislature to pursue the matters dividing his Swedish subjects, and invaded with a mercenary army.