In the beginning of the 19th century the peripheral system—at least in Sweden—was deemed unmodern, due to the extremely long border and coastline of the country, which required a lot of personnel to maintain and support, leading to high costs and a neglect of the more mobile armed forces. The peripheral system was also meant to contain the enemy to a specific area, the coast and borders, but as time went and new tactics were taken into practice, the thin line of fortifications would be easily penetrated by the enemy forces, and when the enemy had advanced through the peripheral line, there would not be enough troops in the hinterland to stop the attacker. The central fortress system was better adjusted to defence in depth, it was not until the enemy attack had reached its culminating point that full counter-attacks would be launched. The central defence had also proven effective in the Seven Years' War—used by Frederick II of Prussia—and in Napoleon's Invasion of Russia—used by the Russians. Carl von Clausewitz, in his military treatise "On War", even mentioned Sweden's good conditions for this kind of war of attrition: