Step 1: Group by period.
One event is from the middle of the twentieth century, one is from the early 1990s and two are from the 2000s. Vietnam War ended in 1975. The Gulf War was in 1990 and 1991. The 9/11 and 26/11 attacks come in the 2000s.
Step 2: Fix the first event.
The Vietnam War ended in 1975, well before the others began. So B must come first. This removes option 1 and option 4, which do not start with B.
Step 3: Fix the last event.
Of the two attacks, 9/11 was in 2001 and 26/11 was in 2008. So D comes before C. This removes option 3, which puts C before D.
Step 4: Check the middle.
The Gulf war of 1990 and 1991 sits between 1975 and 2001, so A comes second.
Step 5: Confirm.
The sequence B, A, D, C fits every date, so option 2 is correct.
Extra check: Why the other options fail.
As a last test, write the four years in a line: 1975, 1991, 2001, 2008. The matching events are Vietnam War, Persian Gulf war, 9/11 attack and 26/11 attack. Read the letters in this order and you get B, A, D, C. No other option follows this line of years.
Final Answer:
The order from earliest to latest is B, A, D, C, which is option 2.
\[ \boxed{\text{2 (B, A, D, C)}} \]