Heat oil on medium heat in a large, deep skillet. Add onion, carrots, and garlic and saute for 1 minute. Add ground beef and pork and continue to cook.
When meat is browned and onions are soft, add tomatoes.
When tomatoes have softened and have started to release their juices (about 4-5 min) add basil, sugar, salt and pepper (if you are whole tomatoes, mash the them with a potato masher or spatula to release all their juices).
Simmer for at least 3 hours (and up to 6 hours), stirring occasionally. The longer you simmer, the better. Important: tomatoes burn easily so keep an eye on them and add beef broth a little at a time to thin sauce if needed.
In a large pot, cook spaghetti in salted water to al dente, drain completely and return to pot. Add sauce to the spaghetti noodles and toss until noodles are covered.