That seems to be "Les Cinq Cents Millions de la Bégum" from Jules Verne.

In Jules Vernes story a princess from India dies and her 500 million are given to a french doctor and a german professor. The french builds a city with modern standards and the german builds a city with huge steel production and cannons. As described in the question the german produces ammunition to kill everyone with gas. And then in the end the german get's killed and his city collapses because he was the one to give orders for everything. The two cities, the cannon, the infiltration, it's all there. The english title is "The Begum's Fortune".

That seems to be Les Cinq Cents Millions de la Bégum from Jules Verne.

In Jules Verne's story, a princess from India dies and her 500 million are given to a French doctor and a German professor. The Frenchman builds a city with modern standards, and the German builds a city with huge steel production and cannons.

As described in the question, the German produces ammunition to kill everyone with gas. And then in the end the German gets killed and his city collapses, because he was the one to give orders for everything.

The two cities, the cannon, the infiltration, it's all there. The English title is The Begum's Fortune.

That seems to be "Les Cinq Cents Millions de la Bégum" from Jules Verne.

That seems to be "Les Cinq Cents Millions de la Bégum" from Jules Verne.

In Jules Vernes story a princess from India dies and her 500 million are given to a french doctor and a german professor. The french builds a city with modern standards and the german builds a city with huge steel production and cannons. As described in the question the german produces ammunition to kill everyone with gas. And then in the end the german get's killed and his city collapses because he was the one to give orders for everything. The two cities, the cannon, the infiltration, it's all there. The english title is "The Begum's Fortune".