If you've ever seen those frequently repeated lists (like these) of historical tragedies against the Jews that happened exactly on the ninth of Av and were ever skeptical of that repeated historical coincidental wonder, this is a blog you must see.
Yutopia investigations shows that most of the events probably didn't happen on the dates they are claimed to have happened. Even for the destruction of the First Temple, sources in Tanach gives two dates, (the seventh and the tenth) neither of which match the ninth. In fact, nowhere in Tanach is the ninth day of the fifth month selected as the day to fast or on which anything bad explicitly happened. It is true that Jews following the destruction of the First Temple fasted and afflicted themselves each year to remember the events, but it is far from clear whether they had a specific day (or a unanimously selected day) on which this occurred.
The point is, however, that it doesn't really matter as far as the purpose of Tisha b'Av goes. Nobody would dare say that the Jews have not suffered a great deal in history and whether or not the Jews suffered specifically on the ninth of Av is immaterial. It is now today the universally identified date on which Jews commemorate the many tragedies that have afflicted us no matter what time of year they took place.
One should not look at Tisha b'Av as a magically unlucky time when metaphysical disfavor showers on the Jews and then search out the history books and current events for additional tragedies to fill up that date. Tisha b'Av should be seen as a day taken out of the year by tradition for Jews to look upon the past, remember the suffering of our ancestors, to identify in some way with their pain and to always move on bravely into the future with the optimism befitting one confident of better times ahead.
May they come bimheira b'yamainu, amen.