Poland did not exist as an independent state prior to1914. When World War I started, Polish territory split during partitions between Austria-Hungary, German Empire and Russian Empire, and millions died.
Poland was invaded by Nazi Germany on 1 September 1939 and by the Soviet Union on 17 September. The campaigns ended in early October with Germany and the Soviet Union dividing and annexing the whole of Poland. After that War the Soviet Union occupied Poland and it was not until 1989 Poland became an independent nation.
With their home in turmoil it is not surprisingly that many young Polish men welcomed the economic freedom and independence offered by the UK Merchant Navy.