Linux - Sort by multiple columns

cat people.txt
#   john; smith; 49
#   amanda; bush; 55
#   john; kidman; 55
#   john; bush; -9
#   amanda; bush; 1
 
# Sort by the 3rd column
sort -t ';' -k3,3n people.txt
#   john; bush; -9
#   amanda; bush; 1
#   john; smith; 49
#   amanda; bush; 55
#   john; kidman; 55
 
# Sort by 2nd, 1st and then 3rd column
sort -t ';' -k2,2 -k1,1 -k3,3n people.txt
#   amanda; bush; 1
#   amanda; bush; 55
#   john; bush; -9
#   john; kidman; 55
#   john; smith; 49