propaganda. Later, numerous scholars have examined the original documents and concluded that large-scale atrocities did occur, while acknowledging that other stories were fabrications. There is a debate between those who believe the German army acted primarily out of paranoia, in retaliation for real or believed incidents involving resistance actions by Belgian civilians, and those (including Lipkes) who emphasize additional causes, suggesting an association with German actions in the Nazi era. According to Larry Zuckerman, the German occupation far exceeded the constraints international law imposed on an occupying power. A heavy-handed German military administration sought to regulate every detail of daily life, both on a personal level with travel restraints and collective punishment, and on the economic level by harnessing the Belgian industry to German advantage and by levying repeated massive indemnities on the Belgian provinces. Before the war Belgium produced 4.4 percent of world commerce. More than 100,000 Belgian workers were forcibly deported to Germany to work in the war economy, and to Northern France to build roads and other military infrastructure for the German army. Historical studies Recent in-depth historical studies of German acts in Belgium include: The Rape of Belgium: The Untold Story of World War I by Larry Zuckerman Rehearsals: The German Army in Belgium, August 1914 by Jeff Lipkes German Atrocities 1914: A History of Denial by John Horne and Alan Kramer. Schuldfragen. Belgischer Untergrundkrieg und deutsche Vergeltung im August 1914 by Ulrich Keller Horne and Kramer describe some of the motivations for German tactics, chiefly (but not only), the collective fear of a "People's War": The same authors identify a number of contributory factors: inexperience leading to lack of discipline amongst German soldiers drunkenness 'friendly fire' incidents arising from panic frequent collisions with Belgian and French rearguards leading to confusion rage at the stubborn and at first successful defense of Liège during the Battle of Liège rage at Belgian resistance at all, not seen as a people entitled to defend themselves prevailing near hatred towards the Roman Catholic clergy in Belgium and France ambiguous or inadequate German field service regulations regarding civilians failure of German logistics later leading to uncontrolled looting Recent studies conducted by Ulrich Keller have put the reasoning of Horne and Kramer into question. Keller claims that the reason for the brutal German behavior in the first few months of the invasion was due to the existence of a substantial Belgian partisan