Former US president Bill Clinton is due to take part in a security conference in Prague on Tuesday that marks the 25th anniversary of NATO’s first eastward enlargement. The former Eastern Bloc states of the Czech Republic, Poland and Hungary joined the transatlantic defence alliance on March 12, 1999, after years of trying to get into the group. Clinton was in the White House when the enlargement took place. He will give a keynote speech at the conference entitled “Our security cannot be taken for granted” on Tuesday at around 1:45 pm (1245 GMT). Clinton, now 77, was the US leader from 1993 to…