This suggestion had some legal plausibility quite apart from the question of the balance of power. For the Prussian garrison held Luxemburg in the name of the German Confederation, which had been destroyed by the war of 1866; and, the authority to which the garrison owed its existence being gone, it was only logical that the garrison should go too. After much demur Count Bismarck acknowledged the justice of the argument (April, 1867), but it did not by any means follow that the French should therefore take the place vacated by the Prussians. At the same time the fortress could not be left in the hands of a weak Power as a temptation for powerful and unscrupulous neighbours. The question of Luxemburg was therefore the subject discussed at a Congress held in London in the following May.
Here the Prussians showed themselves extremely politic and reasonable. Realizing that, with the advance of artillery, the great rock-fortress no longer had the military value of earlier days, they not only raised no objections to the evacuation of Luxemburg by their troops, but in the Congress it was they who proposed that the territory of the Grand Duchy should be neutralized 'under the collective guarantee of the Powers'.[[6]] A treaty was therefore drawn up on May 11, 1867, of which the second article ran as follows:—
'The Grand Duchy of Luxemburg, within the Limits determined by the Act annexed to the Treaties of the 19th April, 1839, under the Guarantee of the Courts of Great Britain, Austria, France, Prussia, and Russia, shall henceforth form a perpetually Neutral State.
'It shall be bound to observe the same Neutrality towards all other States.
'The High Contracting Parties engage to respect the principle of Neutrality stipulated by the present Article.
'That principle is and remains placed under the sanction of the collective Guarantee of the Powers signing as Parties to the present Treaty, with the exception of Belgium, which is itself a Neutral State'.[[7]]
The third article provided for the demolition of the fortifications of Luxemburg and its conversion into an open town, the fourth for its evacuation by the Prussian garrison, and the fifth forbade the restoration of the fortifications.
Such then was the treaty guaranteeing the neutrality of Luxemburg, which was proposed, it may be observed, by Prussia herself; but, until the treaty was broken by the very Power which had proposed the neutrality, only one incident need be noted in the history of the country, namely, the part it played in the war of 1870-1. On December 3, 1870, Count Bismarck issued from Versailles a circular to the Prussian Ambassadors, calling attention to the fact that both the French and the Luxemburgers had violated the neutrality of the Grand Duchy, mainly by giving facilities for French soldiers to return to France. Precautions were taken by the Prussian Government on the frontier to prevent such abuses occurring in the future, and as no violation of the neutrality of Luxemburg was committed by the Prussians, the neutral co-guarantors were satisfied with the Prussian attitude, and the subject dropped. At the end of the war, M. Thiers vainly attempted to obtain Luxemburg as compensation for the loss of Metz.
In accordance with the Family Compact of 1783, the Grand Duchy passed on the death of the late King of Holland to Prince William of Nassau, on whose death the present Grand Duchess succeeded to her father's throne.
There is one point in the Treaty of 1867 which calls for special comment. The neutrality of the Grand Duchy is 'placed under the collective guarantee of the Powers signing'. The phrase originally proposed by Count Bismarck was 'the formal and individual guarantee of the Powers,' and it was altered at the instance of the English Foreign Minister, Lord Stanley. The phrase actually adopted was suggested by the Russian diplomat, Baron Brunnow, and was accepted both by England and by Prussia. Lord Stanley's objection had been based upon the fear that England might incur an unlimited liability to assist Luxemburg single-handed if all other Powers failed to meet their obligations. In other words, Luxemburg might have been used as the infallible means of dragging us into every and any war which might arise between Germany and France. From that danger we were protected by Lord Stanley's objection; as the case stands the treaty gives us, in his own words, 'a right to make war, but would not necessarily impose the obligation,' should Luxemburg be attacked. To this doctrine a reference will be found in the British White Paper (No. 148), where Sir Edward Grey informs M. Cambon of 'the doctrine' concerning Luxemburg, 'laid down by Lord Derby and Lord Clarendon in 1867'. It may also be observed that two of the co-guarantors of the Treaty of 1867, namely Italy and Holland, have also not thought it necessary to make the violation of Luxemburg a casus belli.