Complex sentence: To secure a large majority in the referendum, Schuschnigg dismantled the one-party state; he agreed to legalize the Social Democrats and their trade unions in return for their support of the referendum.
Split into simpler sentences: To secure a large majority in the referendum, Schuschnigg dismantled the one-party state. He agreed to legalize the Social Democrats and their trade unions in return for their support in the referendum.