in between Switzerland and the Tyrol, is included in the customs union of Austro-Hungary.  The small, independent duchy of Luxemburg, which has been attached in turn to all the great states which have grown up along its borders, is included in the Zollverein of Germany.  The republic of Andorra, far up in a lofty valley of the Pyrenees, which has maintained its freedom for a thousand years, acknowledges certain rights of suzerainty exercised by France and the Spanish bishopric of Urgel.[391]

[Sidenote:  Guardians of the marches.]

Oftentimes a state gains by recognizing this freedom-loving spirit of the frontier, and by turning it to account for national defence along an exposed boundary.  In consequence of the long wars between Scotland and England, to the Scotch barons having estates near the Border were given the Wardenships of the Marches, offices of great power and dignity; and their clans, accustomed only to the imperfect military organization demanded by the irregular but persistent hostilities of the time and place, developed a lawless spirit.  Prohibited from agriculture by their exposed location, they left their fields waste, and lived by pillage and cattle-lifting from their English and even their Scotch neighbors.  The valor of these southern clans, these “reivers of the Border,” was the bulwark of Scotland against the English, but their mutinous spirit resisted the authority of the king and led them often to erect semi-independent principalities.[392]

[Sidenote:  Border nomads as frontier police.]

China has fringed her western boundaries with quasi-independent tribes whose autonomy is assured and whose love of freedom is a guarantee of guerilla warfare against any invader from Central Asia.  The Mantze tribes in the mountain borders of Sze-Chuan province have their own rulers and customs, and only pay tribute to China.[393] The highlands of Kansu are sprinkled with such independent tribes.  Sometimes a definite bargain is entered into—­a self-governing military organization and a yearly sum of money in return for defence of the frontier.  The Mongol tribes of the Charkar country or “Borderland” just outside the Great Wall northwest of Pekin constitute a paid army of the Emperor to guard the frontier against the Khalkhas of northern Mongolia, the tribe of Genghis Khan.[394] Similarly, semi-independent military communities for centuries made a continuous line of barriers against the raids of the steppe nomads along the southern and southeastern frontiers of Russia, from the Dnieper to the Ural rivers.  There were the “Free Cossacks,” located on the debatable ground between the fortified frontier of the agricultural steppe and marauding Crimean Tartars.  Nominally subjects of the Czar, they obeyed him when it suited them, and on provocation rose in open revolt.  The Cossacks of the Dnieper, who to the middle of the seventeenth century formed Poland’s border defence against Tartar invasion, were jealous of any interference