This is coolbert:
1. Those French assurances to the Poles, personally from Maurice Gamelin himself, French offensive action to be taken in case of war with Germany indeed to a degree acted upon, but only in a half-hearted and lackadaisical manner, NO punch, best described as a probing action on a massive scale without follow-up, this being the Saar Offensive .
"The Saar Offensive was a French operation into Saarland on the German 1st Army defence sector in the early stages of World War II. The purpose of the attack was to assist Poland, which was then under attack. However, the assault was stopped and the French forces withdrew."
Assistance provided to the Poles, fulfilling the letter BUT NOT the spirit of the promise made by Gamelin. A second-front taking the pressure off the Poles, the German unwilling and perhaps even unable to fight a two-front war, French offensive action  against Germany inexplicably halted, a hasty withdrawal made for reasons unclear!
2. The Western Wall [Siegfried Line] still under construction, the German holding force INSUFFICIENT TO STOP A FRENCH OFFENSIVE IF GAMELIN HAD MOVED FORWARD WITH VIGOR!!
This has been termed the Western Betrayal of Poland!!
From the wiki entry for the Phoney War:
"Both the pre-war reports of the Polish intelligence and the post-war testimonies of German generals (most notably of Wilhelm Keitel and Alfred Jodl) reported that there was an equivalent of less than 20 divisions facing France in 1939, as compared to roughly 90 French divisions. On the other hand, German orders of battle show 33 infantry divisions, plus eleven newly raised infantry divisions, plus the equivalent of six border guard divisions, all under command of Army Group C.
"After the war, General Alfred Jodl commented that the Germans survived 1939 'only because approximately 110 French and English divisions in the West, which during the campaign on Poland were facing 25 German divisions, remained completely inactive.'"
3. That French Air Force [Armée de l'Air] in 1939 both qualitatively and quantitatively inferior to the German. That one fighter/interceptor most relied upon by the French found to be wanting and generally speaking inferior the German Me-109.
"The M.S.406 was a French Armée de l'Air fighter aircraft built by Morane-Saulnier starting in 1938. Numerically it was France's most important fighter during the opening stages of World War II."
"it was under-powered and weakly armed when compared to its contemporaries. Most critically, it was out-performed by the Messerschmitt Bf 109E [Me-109] during the Battle of France . . . when the war restarted in earnest in 1940 [Battle of France], 387 were lost in combat or on the ground . . . for 183 kills in return."
* That French Armée de l'Air did NOT exist in a vacuum. Did have considerable reinforcement from the British Royal Air Force [RAF]. That English Spitfire fighter/interceptor however not having quite the performance during the Battle of France as it did several months subsequent! At least not until the arrival of American high-octane aviation gasoline [AVGAS] boosted the performance of the Spitfire considerably.
* Please be very careful when comparing those statistics of German divisions available to Hitler opposite the French ! When Jodl speaks of twenty to twenty-five divisions he means fully manned, fully trained, fully equipped divisional sized contingents organized into fully manned, fully trained units at a high degree of readiness - - combat ready - - fully capable of operations beyond corps and army level as an integrated force. Additional units of divisional size more than likely NOT combat ready. Present but NOT prepared for combat as per exacting German army standards. Such is the difficulty in making order-of-battle estimates and evaluations.