Strategy

Try to attack where they are not expecting it. Try to check if they have any navy by checking if they built any naval bases. If they don't have naval bases, you can make some convoys and attack their core provinces or at an unexpected place far from the front lines. Then, if they make the mistake of not leaving units to protect their core [rpvinces, you can easily conquerer their important cities and resource provinces, which will damage their economy and allow you to win.

Mustafa 33 wrote:

I want some attrition strategies that quickly defeat the opponent

1. Wither down your opponent as he advance to your territory

2. Deny him of every provisions and advantage he has at your territory

3. Slow him

4. Avoid direct confrontation with your opponent

5. Like a shadow appear only when necessary

6. Damage him as he moves

7. Attack only when his forces are weakened

8. Be maneuverable

It is different from Blitz or blitzkrieg where

1. You steamroll your enemy with superior force and firepower

2. Move quickly as possible

3. Deny your enemy movement as possible

4. Surround and encircle

5. Destroy him

Attrition warfare is asymmetrical warfare. This is similar to what the Taliban and Viet Cong did. You need both patience and understanding of your opponent's abilities, movements and battle plan in order for you to pull it out. You cannot quickly win a war with attrition sadly.