Well, the AI is not always going to sit back and "not let you fight"...but there are ways to minimize the amount of fighting you have to actually do. Cheap leg infantry and towed arty will usually be enough to make this work, so it can be set up pretty quickly, even by poorer countries. As I mentioned, once one country attacks you, you "usually" have some breathing room before anyone else will rebuild enough Belli to follow suit. (Unless you are the United States or Germany or someone else that pisses everyone else off very easily. In which case, declarations of war can happen in cascading "avalanches") Oh, some fighter/bombers and attack helos can be a very big help in this tactic too.
Choose a line of defense. Towns, factories, bases, and bridges make good defense points, but if you have to, open ground will work. As quickly as possible, build stacks of the toughest leg infantry (I prefer marines) and hardest hitting towed arty you can. 3-4 Inf, and 3 arty. Space these along your defense line close enough to support each other, preferably with overlapping arty fire in between them. Stage FBs, helos, tanks and mech infantry behind this defense line to reinforce any spot that gets in more hot water than it can handle.
Ok. So far this sounds like first grade beginner strategy...correct? Here is how it relates to the AI in 2010. If you can keep the enemy from crossing this line... you do not counterattack. Do not take possession of one single hex that the enemy has grabbed. After the AI has run out of steam attacking you, it will almost literally ignore you, if you do not take possession of any hex that they control. After a couple weeks of fighting, you can basically ignore this border. The AI may send the odd unit sniffing around, but it will not repeat any all out attacks. This is why it is very important to set up your line to hold everything you want to retain, because even the smallest counter attack will stir up the hornet's nest all over again. I often use this "stalemate" in the middle of invading a large enemy to catch my breath and repair/reinforce/reorganize my forces.
True, you will have to remain on defcon 3 and pay the money to remain there, but if you do not want to invest troops and attention, you can relax and build up your forces. Which brings us to the only sure fired way to speed up the AI's belli. Increase your buildcap. Upgrade the bases you have to larger sizes, build new ones. Even if you can't afford to build 64 tank brigades at one time, the AI will resent you being capable of this and eventually attack.
I hope this helped some,
"Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery.” -Winston Churchill