Agreements with foreign States concerning alteration of the national frontiers shall be concluded by the Realm after the Land affected has given its consent. Frontier alterations can be effected by act of the Realm only, except in mere rectifications of frontiers in uninhabited districts. The Realm shall take the necessary measures and make the necessary arrangements, in agreement with the Lands affected, to safeguard such interests of those Lands as may be involved in their peculiar economic connections with or in their geographical contiguity to foreign States. ARTICLE 79. National defence is an affair of the Realm. An act of the Realm shall uniformly regulate the military constitution of the German people, with due regard for local conditions. ARTICLE 80. Colonial affairs pertain exclusively to the Realm. ARTICLE 81. All German merchant vessels constitute a united mercantile marine. ARTICLE 82. Germany constitutes a Customs and Commercial Union enclosed in a common customs frontier. The customs frontier coincides with the foreign frontier. Towards the sea the continental coast line with the islands belonging to the Realm forms the customs frontier. Deviations may be admitted where the customs frontier reaches the sea or other waters. The territory of foreign States, wholly or partly, may be included within the Customs Union by treaty or other agreement. Parts of the Union may be excluded under special necessity. In the case of free harbours such exclusion can be terminated only by constitutional amendment. Territories excluded from the Union may be joined to a foreign Union by treaty or by agreement. All products of nature, industry and art in free circulation within the Realm may be exported, imported, or transited across the frontiers of the Lands or local communities. Exceptions to this may be made by act of the Realm. ARTICLE 83. The authorities of the Realm shall administer all tariffs and all indirect taxes.[31] Where the authorities of the Realm administer national taxation, provision shall be made preserving to the Lands their peculiar interests in the sphere of agriculture, commerce, manufacture, and industry. ARTICLE 84. The Realm shall, by legislation, regulate:-- (1) Financial administration within the Lands in so far as required in the interests of the uniform execution of the national fiscal laws; (2) The organisation and functions of the authorities entrusted with the execution of the national fiscal laws; (3) Accountancy between the Realm and the Lands; (4) Re-imbursement of the costs of fiscal administration. ARTICLE 85. All income and expenditure of the Realm must be estimated yearly and incorporated in the Budget. The Budget shall be passed as an act before the opening of the financial year.