I play without national objectives regularly. IMHO, the key for the Axis is killing Russia. I have found that the best way to kill Russia is to do a combined Germany/Japan land assault. However, this cannot be done if USA and GB are offloading on France/NWE- Germany cannot guard the Atlantic borders and keep pressure on Russia. My solution was simple. Establish a chain supply of Japanese fighters to France for defense (2 per turn as of turn 3) This accomplishes two things: one, defends France effectively and,two, forces the Allies to build navy to avoid losing their transports. This allows Germany to send roughly half of their land forces to the Russia front. ( build only infantry and artillery since IPC’s are scarce from turn 3 forward) This slows Japan down but is well worth it to keep pressure on Russia from Germany. Also, move the Japanese fleet to protect Italy from invasion. Allies can’t amphibious assault Italy with a massive combined Italian/Japanese fleet in sea zone 14.
I build a German bomber on turns 1 & 2 to keep Britain off shores till turn 3, then the bombers become useful in swapping territories with Russia.