G. A. Henty 
With Frederick the Great 

Historical novel, set in Prussia and elsewhere in Europe in the middle of the 18th century. The Preface begins: 'Among the great wars of history there are few, if any, instances of
so long and successfully sustained a struggle, against enormous odds, as that of the Seven Years’ War, maintained by Prussia–then a small and comparatively insignificant kingdom–against Russia, Austria, and France simultaneously, who were aided also by the
forces of most of the minor principalities of Germany. The population of Prussia was not more than five millions, while that of the Allies considerably exceeded a hundred millions. Prussia could put, with the greatest efforts, but a hundred and fifty thousand men into the field, and as these were exhausted she had but small reserves to draw upon; while the Allies could, with comparatively little difficulty, put five hundred thousand men into
the field, and replenish them as there was occasion.’ According to Wikipedia: 'George Alfred Henty (8 December 1832 – 16 November 1902), referred to as G. A. Henty, was a prolific English novelist, special correspondent, and Imperialist born in Trumpington, Cambridgeshire, England. He is best known for his historical adventure stories that were popular in the late 19th century. His works include Out on the Pampas (1871), The Young Buglers (1880), With Clive in India (1884) and Wulf the Saxon (1895).’