German politicians are vowing tougher laws to protect investors following the collapse of a wind farm company that exposed investors to potential losses of €1.4 billion ($1.9 billion). Chancellor Angela Merkel said Thursday that the government will strengthen securities rules after Prokon Regenerative Energien GmbH firm filed for insolvency potentially leaving losses for about 70,000 private investors. Ms. Merkel has campaigned ardently for tighter regulation of global markets since the 2008 financial crisis. But the collapse of Prokon shines a light on weaknesses in securities rules closer to home.