Some 20,000 soldiers from 10 NATO countries were readying on Monday to cross Poland’s longest river, the Vistula, as part of a manoeuvre aimed at deterring Russian aggression. The Dragon 24 drill will take place near the town of Korzeniowo, about 100 kilometres south of Gdańsk. About 15,000 of the participating soldiers will come from Poland, according to Warsaw. The crossing of the Vistula with the construction of a pontoon bridge will test the ability of land, sea, air and cyber forces to work together during a major military crisis, the Polish armed forces said. There are increasing warning…