I think it has already been said before but these counter-insurgency wars don't really work out well:
The people the west fight against are in their own country, this means they know the terrain and local environment much better than the foreign troops and can use this to their advantage. For instance in the Vietnam war the guerrila fighters (the Vietcong) used tunnels through the jungles and create networks of trading paths (the ho chi minh trail) that were undetectable by the American soldiers. They could also plant mines that injured unsuspecting american soldiers yet their own fighter were safe miles away in their tunnels. This demoralised and fustrated the Americans which was a contributing factor for them loosing the war. Similerly in the Afganistan and Iraq wars the insurgents knew all of compound areas which allows them to escape from the allied forces if they were pinned down by fire. They also have extensive knowledge of which areas are heavily booby trapped with IEDs and such weapons so can avoid them themselves and lead the allies into a area riddled with mines.
Secondly, the insurgents are not part of a formal army which represents a country. Therefore they wear no uniforms and thus it makes it impossible to distinguish between the local people and the people you are fighting. In the vietnam war this led to thousands of civilians being kiled by the american soldiers and this undermimed the US's 'hearts and minds' strategy. This eventually led to the americans withdrawing as they were becoming increasingly unpopular with the locals and the media covergae of innocent civilians being napalmed and killed reduced support for the war back in america. In more modern conflicts such as the Afghanistan war, British and american soldiers have to PID (positivelt identify) their targets before they can fire. This means that they can only retalliate to the enemy if the enemy shoots first or if they feel clearly in danger. This is to try and prevent civilian casulties however it frustrates soldiers as the insurgents don't follow any rules of combat so they have the advantage in a theatre situation. It is also very hard to tell which locals support the foreign troops or not and understandably the locals change their minds quickly and if for instance the taliban is threatening their families they will support the taliban to try and keep their families safe. The lcoals are often concerned as well as to what will happen to them if support the foreign soldiers against the taliban when the foriegn soldiers withdraw. Look for instance at what is happening right now to those afghan translators who worked for the British army.
Finally, the foreign soldiers are not in their own country and as wars don't last forever at some point they will have to withdraw. The insurgents however are still in the country and will continue fighting. For example after the Americans withdrew from Vietnam the communists who they had been fighting captured Saigon (now Ho chi minh city) as the South vietnamese army who the Americans wanted to take over the war, were too weak on their own without american manpower and finance. Similarly, at present the Taliban are taking over areas that the allies fought to capture as the ANA are too weak on their own to stop them. The weapons and equipment left behind after a war can also benefit the enemy if it falls into their own hands.
Overall i do not think that conventional warfare works to fight an ideology and not a country as history has shown us that these wars often create more politcal unrest and resentment and that the formal armies often lose or their is no clear victory.