Worldwide, many sizes of tank were considered, and much of the development effort went into light tanks that were useful primarily against infantry or for colonial police-type work. The worldwide economic difficulties of the 1920s and 1930s led to an increased emphasis on light tanks as they were much cheaper to produce than medium or heavy tanks. However, the Spanish Civil War showed that tank-versus-tank engagements and tank-versus-towed antitank gun engagements would now be a major consideration for the future of tank warfare. It became clear that tanks would need to be heavily armoured and carry larger guns. Tank shape, previously guided purely by considerations of obstacle clearance, now became a trade-off between a low profile, desirable for stealth, and weight savings.