[1] In the middle of the nineteenth century the government of Carlos Antonio López, determined to open up Paraguay to modern technology, hired for that purpose a considerable number of technicians, mainly British.

[2] In September 1858 Thompson joined the staff of the Asunción–Villarica railway in Paraguay, working under the British engineers George Paddison, Burrell and Valpy.

[1] After the war between Paraguay and the allied forces of Brazil and the Argentine and Uruguayan Republics broke out, Thompson offered his services as a military engineer to the Paraguayan President, Francisco Solano López, in 1865.

Furthermore, throughout the war, Paraguay's nominal chief military engineer, Hungarian colonel Wisner de Morgenstern (who had designed the Fortress of Humaitá) was seriously ill, and so the work fell on Thompson's shoulders.

Since Thompson had been the foreigner with best access to President López – from whom he took his orders in Guaraní[8] – and privy to many military matters, the book is an important source on the history of the war,[9] one of the earliest of its kind and widely used by later historians.