Industrial districts of modern Europe, such as England, Belgium, Saxony, Departments Nord and Rhone in France, show a density of 500 to 800 to the square mile.

[See maps pages 8 and 9.] [Sidenote: Density of population and government.] With every increase of the population inhabiting a given area, and with the consequent multiplication and constriction of the bonds uniting society with its land, comes a growing necessity for a more highly organized government, both to reduce friction within and to secure to the people the land on which and by which they live.

Therefore protection becomes a prime function of the state.

It wards off outside attack which may aim at acquisition of its territory, or an invasion of its rights, or curtailment of its geographic sphere of activity.

The modern industrial state, furthermore, with the purpose of strengthening the nation, assists or itself undertakes the construction of highways, canals, and railroads, and the maintenance of steamship lines.