Meanwhile a struggle had broken out as to the succession in Upper Bavaria. By a treaty made in 1349 between the sons of Lewis the Bavarian, that duchy ought now to have gone to Lewis the Roman and Otto, in whose favour their elder brother Lewis had renounced the possession of Brandenburg. But the second brother, Stephen of Lower Bavaria, anticipated their claim and obtained his own recognition from the estates of Upper Bavaria. The two margraves applied for assistance to Charles IV., and promised him the succession to Brandenburg if they died without heirs. This agreement ultimately took effect in 1373, when Otto, the surviving margrave, was induced or compelled to cede Brandenburg to the Emperor, who pledged himself to the estates that the union of Brandenburg with Bohemia should be perpetual. Thus Charles acquired a second electoral vote and a very notable increase of his territorial power in northern Germany. About the same time he betrothed his second son, Sigismund, to the daughter of Lewis the Great, King of Hungary and Poland, and thus opened a prospect of adding these states to the now enormous possessions of the Luxemburg House. These actual or prospective acquisitions could be of little permanent value unless Charles could secure to his House the continued occupation of the imperial office, and in 1374 he began to sound the electors on the subject [Sidenote: Election of Wenzel.] of the election of his son Wenzel, a boy of fifteen years old. But there were many difficulties in the way. The Golden Bull made no provision for an election during the lifetime of any occupant of the throne. The spirit, if not the letter, of the law was against such a thing. There were also serious objections to the election of a minor, and many princes were jealous of the predominance already gained by the Luxemburgers. Charles, however, was not very scrupulous in such a critical matter, even about the observance of his own laws. He gained over the electors, but by the old objectionable method of bribing them. He did not hesitate to appeal for papal approval, thus reviving the pretensions which the Golden Bull had practically abrogated. But his policy was successful in its immediate aim. Wenzel was elected at Frankfort on June 16, and crowned at Aachen on July 6, 1376.