Turkey, under a law proclaimed in 1869, prohibited the naturalization of its subjects abroad without the permission of the Turkish government. The penalty provided was imprisonment or expulsion.[24] In practice, however, expulsion has been the only penalty inflicted, and the United States has contented itself with an occasional protest. The practice of Greece is not entirely clear-cut or consistent. A law enacted in 1914 requires the permission of the government before naturalization abroad; in practice this is not given to those who have not discharged their legal obligations as to military service.[25] The practical effect of this attitude on the part of Greece has been shown chiefly in the failure of Greeks in this country quite generally to seek naturalization. CONDITIONAL RECOGNITION The obligation which these countries commonly require as a prerequisite to permission is that of military service for the required period. Perhaps the best example of this group is France, which has provided by law that its nationals may divest themselves of their French citizenship provided they are thirty-one years of age, and thus may be presumed to have complied with the conditions of military service.[26] The other countries requiring similar conditions are Italy, the Netherlands, Serbia, and Switzerland; the usual penalty being liability to arrest upon return, and the compulsory fulfillment of the military requirements. But Switzerland provides for an annual tax in lieu of the military requirement. The United States government has repeatedly sought through diplomatic channels to secure mitigation of penalties inflicted by these countries on its naturalized citizens; in many cases with a greater or less measure of success; but it has been unable to secure by treaty with any of these countries an unconditional recognition of the right of expatriation. NATURALIZATION TREATIES WITH THE UNITED STATES