His personal allegiance to Lutheranism was sound, but he liked neither the growing strength of Brandenburg-Prussia nor the increasing prestige of the Palatinate; the adherence of the other branches of the Saxon ruling house to Protestantism seemed to him to suggest that the head of the Electorate of Saxony should throw his weight into the other scale, and he was prepared to favour the advances of the Habsburgs and the Roman Catholic party.

[2] Thus John George was easily induced to vote for the election of Archduke Ferdinand of Styria, as emperor in August 1619, an action which nullified the anticipated opposition of the Protestant electors.

[2] Gradually, however, he was made uneasy by the obvious trend of the imperial policy towards the annihilation of Protestantism, and by a dread lest the ecclesiastical lands should be taken from him; and the issue of the Edict of Restitution in March 1629 put the capstone to his fears.

Marching into Bohemia the Saxons occupied Prague, but John George soon began to negotiate for peace and consequently his soldiers offered little resistance to Wallenstein, who drove them back into Saxony.

However, for the present the efforts of Gustavus Adolphus prevented the elector from deserting him, but the position was changed by the death of the king at Lützen in 1632, and the refusal of Saxony to join the Protestant league under Swedish leadership.

[2] Still letting his troops fight in a desultory fashion against the imperials, John George again negotiated for peace, and in May 1635 he concluded the important Treaty of Prague with Ferdinand II.

At length in September 1645 the elector was compelled to agree to a truce with the Swedes, who, however, retained Leipzig; and as far as Saxony was concerned this ended the Thirty Years' War.