In that year Napoleon III had anticipated that the war between Prussia and Italy on one side and Austria and the small German states on the other would be long and exhausting, and would end in France imposing peace on the weary combatants with considerable territorial advantage to herself.  His anticipation was entirely falsified; the war lasted only seven weeks and Prussia emerged victorious and immensely strengthened by the absorption of several German states and by the formation of the North German Confederation under her leadership.  This, the first shattering blow which the French Emperor’s diplomatic schemes had received, led him to demand compensation for the growth of Prussian power, and one of his proposals was the cession of Luxemburg to France.

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.