 Complete the following phrase:  The Interwar period was dominated by the strategic thinking with fortified borders at its core. These included obstacles consisting of natural features such as ditches, streams and urban areas, or constructed obstacles such as anti-tank ditches, minefields, dragons teeth, or log barriers. The pinnacle of this strategic thinking was considered to be the Maginot Line which replaced infantry-filled trenches with artillery-filled bunkers, including casemates housing 37 or 47 mm anti-tank guns, and steel turrets armed with a pair of machine guns and a 25 mm anti-tank gun, although Germany was forbidden to produce tanks. The construction was partially based on the Allied experience with the Hindenburg Line which was breached with tank support during the battles of Cambrai and St. Quentin Canal, although German Command was more impressed by the surprise achieved by the Canadian troops at the 