Fiat Chrysler Automobiles NV and PSA Group are poised to get shareholders' sign-off on a combination that's endured two years of extraordinary drama, marked by on-again off-again talks, the transformation of their industry and a global pandemic. At two separate meetings Monday, investors will be asked to approve a merger that will form Stellantis, the world's fourth-largest automaker. The hurdles the two overcame to get to this point were plentiful and prodigious, with Fiat even managing to patch things up after a short-lived attempt to join forces with PSA's archrival Renault SA. Fiat Chrysler and PSA executives reckon they'll boost returns with scale more closely resembling Volkswagen AG and Toyota Motor Corp., and have greater resources to compete with electric-car upstarts and tech-industry interlopers. But plenty of challenges await once the deal is done. Stellantis will be an amalgam of model lines with enviable positions in certain segments and areas of the world, but neither company has much of a foothold in the luxury-car business or China's vast auto market.