▁in ▁the ▁family ▁business . ▁In ▁ 1 9 0 6 ▁Lé once ▁ ▁and ▁his ▁brother ▁inherited ▁the ▁family ▁gallery ▁on ▁Avenue ▁de ▁l ' Op éra ▁which ▁had ▁been ▁in ▁existence ▁for ▁twenty ▁years . ▁His ▁brother ▁Paul ▁was ▁largely ▁engaged ▁in ▁ 1 9 th - ▁and ▁early ▁ 2 0 th - century ▁art . ▁ ▁Lé once ▁Ros enberg ▁was ▁an ▁early ▁advoc ate ▁of ▁Cub ism , ▁and ▁would ▁remain ▁so ▁throughout ▁the ▁ 1 9 2 0 s ▁and ▁ 1 9 3 0 s . ▁He ▁discovered ▁the ▁works ▁of ▁avant - gar de ▁artists ▁in ▁ 1 9 1 1 ▁through ▁the ▁Sal on ▁des ▁Ind ép end ants , ▁the ▁art ▁deal er ▁Wilhelm ▁U h de , ▁and ▁in ▁ 1 9 1 2 ▁at ▁the ▁gallery ▁of ▁Daniel - Hen ry ▁K ahn we iler . ▁ ▁At ▁the ▁out set ▁of ▁World ▁War ▁I ▁many ▁German ▁national s ▁living ▁in ▁France ▁had ▁their ▁poss essions ▁se quest ered ▁by ▁the ▁French ▁state . ▁As ▁a ▁German ▁citiz en ▁K ahn we iler ▁took ▁refuge ▁in ▁Switzerland ▁and ▁ran ▁out ▁of ▁funds . ▁With ▁his ▁art ▁collection ▁the ▁hand ▁of ▁the ▁French ▁government ▁he ▁could ▁no ▁longer ▁support ▁his ▁artists . ▁Following ▁the ▁advice ▁of ▁Max ▁Jacob ▁and ▁André ▁Level ▁( known ▁for ▁his ▁well ▁informed ▁art ▁invest ments ), ▁Lé once ▁Ros enberg ▁began ▁am ass ing ▁his ▁collection . ▁Just ▁before ▁the ▁out break ▁of ▁World ▁War ▁I ▁Ros