It would be quite invaluable if, supposing there were to be war (arising from this or other causes), Spain could be persuaded to join in the attack on France and act the part which Italy had played in 1866.
What he probably hoped for more than anything else was that France would declare war against Spain; then Napoleon would waste his strength in a new Mexico; he would no longer be a danger to Germany, and whether Germany joined in the war or not, she would gain a free hand by the preoccupation of France.

If none of these events happened, it would be an advantage that some commercial gain might be secured for Germany.
On the whole, the affair is not one which shews his strongest points as a diplomatist; it was too subtle and too hazardous.
The news aroused the sleeping jealousy of Prussia among the French people; the suspicion and irritation of the Government was extreme, and this feeling was not ill-founded.

They assumed that the whole matter was an intrigue of Bismarck's, though, owing to the caution with which the negotiations had been conducted, they had no proofs.

They might argue that a Prussian prince could not accept such an offer without the permission of his sovereign, and they had a great cause of complaint that this permission had been given without any communication with Napoleon, whom the matter so nearly concerned.

The arrangement itself was not alone the cause of alarm.