To Barbarossa
Between the Polish and Western campaigns the Reich had already taken steps to secure its northern and southern flanks. Operations in Denmark and Norway secured Swedish iron ore deliveries and Romania agreed to sell more of its oil. But now even before France signed its armistice all of Europe realized a new, German-centered geopolitical reality was at hand and adapted to it. Italy joined the war and Romania gave Germany a monopoly on its oil. Even Spain and Portugal became slightly friendlier. Switzerland offered more generous terms on trade.
Berlin was now the heart of a power bloc backed by the economies of occupied, neutral and allied states, and beyond them, the resources of the Soviet Union. Facing it was the British Empire backed by America, and the question remained on how to deal with this troublesome archipelago.

Hitler still hoped for a settlement with Britain, leaving it to its empire while becoming the hegemon on the continent, but his overtures were rejected due to British confidence in American aid. To reach such a deal he’d need to deal a strong enough blow to the British and do so before a full American entrance in the war. There was thus a time window at hand.
A cross-Channel invasion was out of the question. The Kriegsmarine’s surface ships were hopelessly outmatched and their inferiority only widened after heavy losses in Norway. Planned battleships would take years. All that could be done was harass British supply lines through battlecruisers and U-boats. It was too late to invest in the former. The latter were few in number due to the priority given to bombers and ammunition since the start of the war, and only gained a higher priority for a brief period. U-boat numbers declined to a bottom of 22 in February 1941. Though plenty of convoy tonnage was sunk it was far from enough and American aid aswell as decryption and new convoy tactics tilted the balance at sea against the Axis. Worse of all, Doenitz estimated that even with an ideal number of U-boats, it’d take until autumn 1941 to isolate Britain and more months to starve it out, and this was beyond the time window.
The Luftwaffe was the other arm that could be used. However, it had just lost nearly 30% of its strength in the French campaign. The Ju 88 had neither the numbers nor the specifications to win the campaign. Its dedicated escort, the Me 110, proved a failure. Heavy bombers would’ve been valuable but of the existing project, the He 177, only 500 were in order and they’d come in 1941-2. (When they did, the aircraft was a disappointment). Damage was dealt but the air war could not bring victory.
In short, there was never any chance of bringing Britain to its knees. The British, on their part, had no way to invade the European mainland, either. As many predicted years in advance, the war reached a stalemate; the unexpected fact was just that it was at the Channel rather than on France. The only ones who could benefit from this were America and Russia. The latter, it is noted, tallied up the total number of aircraft lost over England without breaking them down by side: all that mattered was that the two exhausted themselves.