Clean Lines, Open Spaces: A View of Mid-Century Modern Architecture: "Clean Lines, Open Spaces: A View of Mid-Century Modern Architecture" focuses on the construction boom in the United States after World War II. Sometimes considered cold and unattractive, mid-century modern designs were a by-product of post-war optimism and reflected a nation's dedication to building a new future. This new architecture used modern materials such as reinforced concrete, glass and steel and was defined by clean lines, simple shapes and unornamented facades.