In the 19th century, it became desirable for all nations of Europe (and later worldwide) to identify a national flag. During that time, the terms Britain and England were used largely interchangeably, the Union Flag was used as national flag "de facto", even though never officially adopted. The observation that the Cross of St George is the "national flag of England" (as opposed to the Union Flag being the flag of all of the United Kingdom) was made in the context of Irish irredentism, as noted by G. K. Chesterton in 1933,