Do the countries schedule holidays on the same days on purpose? so ,many of these holidays fall on the same day as each other they must.
Each day during the London session 60% of all trading for the entire day is done. So when London is on holiday you can expect significantly lower volume. Add in the U.S. holiday and you got the perfect recepie for a slow boring trading day and maybe some unexpected erratic movements. On days like this I back away from the market and relax, it is a holiday Monday, forget about trading and enjoy your long weekend. I will put up the weekly analysis tomorrow ready for the beginning of the real trading week.