Let's start with Buchanan's first point that the entire war started merely because of a small Polish town with German speaking citizens:
Why did Warsaw not negotiate with Berlin, which was hinting at an offer of compensatory territory in Slovakia? Because the Poles had a war guarantee from Britain that, should Germany attack, Britain and her empire would come to Poland’s rescue.
But why would Britain hand an unsolicited war guarantee to a junta of Polish colonels, giving them the power to drag Britain into a second war with the most powerful nation in Europe?
Buchanan sets this up be glossing over what lead up to this point. France and Britain watched on, at first disinterested but then increasingly uneasy, as Germany very rapidly rebuilt a military that was outlawed under Versailles and swallowed, sometimes at the allowance of both nations, to gobble up a vast tract of central Europe. As the the dominoes of Alsace-Lorraine, Austria, and Czechoslovakia tumbled and Germany became much more militarily bellicose, France and Britain had every right to be concerned about Germany's intentions. Taking a stand at Poland was not a Franco-Anglo hair trigger for war. Germany had already re-acquired many German speaking areas. If Germany did not have expansionist plans, Poland would have been a good place to stop, or even limit their Polish excursion to Danzig, which would have put Britain and France in an awkward position.
Next, Buchanon asks a series of questions that the answers to which he pretend don't exist in order to create the doubt he wants in his readers minds. Let's take them one at a time.
why did he spend three years building that hugely expensive Siegfried Line to protect Germany from France?
Germany was very well aware that it was vulnerable to a two front war. German doctrine was to stabilize one front while fighting a more vigorous battle on the other front. The Siegfried Line was part of that strategy. It was meant to stabilize the Western Front, freeing more supplies and men to fight on the Eastern Front. The fact that it never played out that role is due to Hitler's impatience and poor strategic thinking.
Why did he start the war with no surface fleet, no troop transports and only 29 oceangoing submarines?
One does not conquer the world in a day, even an impatient dictator such as Adolf Hitler. And even Hitler realized the limitations involved in one nation conquering the entire world, hence the alliance with Japan. The fact is, mainland Europe and the British Isles were the first targets in his sights. By quickly decapitating France, Britain, and Russia, Germany would leave their empires vulnerable in other lands. The fact is, in order to accomplish this, Germany did not need a huge surface fleet, at least not right away. If Germany had been able to quickly take out Britain through air warfare, they would have had the security on their western front to allow them to swing resources toward the USSR. They also would have been in unmolested possession of many advanced shipyards in Britain, Western Europe, and Northern Europe with which to build a fleet for future engagements far ashore.
Had Hitler waited until he had built a fleet to compete with the British, he'd have forfeited the advantage that he had built by quickly re-arming and shoving his way into new lands across the European Continent. He'd have also given France and Britain extra time to build up their own militaries in anticipation of a conflict with Germany. All Germany really need at this stage was u-boats to harass shipping and enemy fleets. And remember, the German U-boats and their fleets still did outclass anything the allies had. Additionally, Germany had a total of 65 U-boats at the outset of war. 29 were oceangoing, but they had a lot more about to go on line.
How do you conquer the world with a navy that can’t get out of the Baltic Sea?
You don't, but again, stage one wasn't about conquering the world. It was about conquering Europe. Germany, laying in the west-central region of the continent, did not need a massive surface navy. Not yet, anyway. In light of that goal, a massive Navy seems a waste of resources, no?
If Hitler wanted the world, why did he not build strategic bombers, instead of two-engine Dorniers and Heinkels that could not even reach Britain from Germany?
Again, he did not need strategic bombers, not yet. Germany clearly intended to quickly destroy Britain through bombings from France. There was no need for strategic bombers. If Germany does not hold France, then going after Britain is pointless. And Germany very well may have taken Britain out of the war had they not made a very significant strategic error-initiating war in the east.
Why did he let the British army go at Dunkirk?
Why did he offer the British peace, twice, after Poland fell, and again after France fell?
Nobody is really sure to this day, but the smart money is something that Buchanan himself brings up later in the article:
...and that meant war with Britain, whose empire he admired and whom he had always sought as an ally.
The Germans and the Brits are ethnic cousins. In Hitler's twisted ethnic world view, that made them acceptable, if subordinate, allies. He very likely was giving Britain a chance to seek peace by becoming a subordinate partner to Germany, saving the German military from having to expend money, men, and material on Britain.
Why, when Paris fell, did Hitler not demand the French fleet, as the Allies demanded and got the Kaiser’s fleet? Why did he not demand bases in French-controlled Syria to attack Suez?
They were not critical and they were not going to be handed over as simply as Buchanan implies. The British sunk ships that they suspected were not Free French, and at times, French sailors scuttled their own ships.
Why did he beg Benito Mussolini not to attack Greece?
Germany was preparing for Operation Barbarossa, and any Italian failure in Greece could be problematic for the planned invasion of the USSR. It is tough to be preparing for war while at the same time wishing an ally not to attack because you want war to be over.
I do not for a minute believe that Buchanan is so dim as to not understand the facts on as they were in this period. I do believe that, because of his isolationism and his hostility towards Jews, Buchanan does want to diminish World War II in the eyes of the public. Unfortunately, for many with a thin understanding of the war, he does have some success.
In light of Buchanan's Polish question, I did want to also share a snippet from the memoirs of Albert Speer, Nazi Germany's Minister of Armaments and War Production:
On May 2, 1938, Hitler drew up his personal will. He had already outlined his political testament on November 5, 1937, in the presence of the Foreign Minister and the military heads of the Reich. In that speech, he referred to his extensive plans for conquest as a "testamentary bequest in case of my decease." With his intimate entourage, who night after night had to watchtrivial operetta movies and listen to endless tirades on the Catholic Church, diet recipes, Greek Temples, and police dogs, he did not reveal how literally he took his dream of world dominion. Many of Hitler's former associates have since attempted to establish the theory that Hitler changed in 1938. They attribute the change to his deteriorated health resulting from Morell's treatment. It seems to me, on the contrary, that Hitler's plans and aims never changed. Sickness and fear of death merely made him advance his deadlines. His aims could only have been thwarted by superior counterforces, and in 1938 no such forces werte visible. Quite the opposite: The successes of that year encouraged him to go on forcing the already accelerated pace. [Albert Speer, Inside the Third Reich (The Macmillan Company, 1970), 106-107]
Doesn't sound like a man who was ready to settle for just the reconquest of German speaking lands to me.