Montesquieu
 

IX.2 That the federative constitution must be composed of states of the same kind, especially of republican states

The Canaanites were des­troyed because they were small monar­chies which had not confe­de­ra­ted, and did not defend them­sel­ves in com­mon. For confe­de­ra­tion is not the nature of small monar­chies.

The fede­ra­tive repu­blic of Germany is com­po­sed of free cities and small sta­tes under the rule of prin­ces. Experience shows it to be more imper­fect than those of Holland and Switzerland.

The spi­rit of monar­chy is war and aggran­di­ze­ment ; the spi­rit of the repu­blic is peace and mode­ra­tion. These two kinds of govern­ment can­not coexist except by force in a fede­ra­tive repu­blic.

Thus we see in Roman his­tory that when the Veientes1 had cho­sen a king, all the small repu­blics of Tuscany aban­do­ned them. All was lost in Greece when the kings of Macedonia obtai­ned a posi­tion among the Amphictyonies.

The fede­ra­tive repu­blic of Germany, com­po­sed of prin­ces and free cities, sub­sists because it has a head, who is in some sense the magis­trate of the union, and in some sense the monarch.

[The inhabitants of Veii, an Etruscan city.]