German ambassador: Obama agreed not to send arms to Ukraine

Thing is from Germanys perspective delivering weapons into the Ukraine - or indeed taking a singular hardline stance against Russia - would hurt Ukraine more than they help. Reasoning being as follows:

Russia is and has since the attack on the Crimean Peninsula been waging a limited war against the Ukraine similar to a number of conflicts we have seen earlier.
Russia thus is currently not totally committed to this war nor has an interest to significantly expand it. It has significant reserves which it currently doesn't plan to invest.

This situation would change the moment weapons were delivered in large scale from the west. The reasoning behind this is a bit more versatile and I won't go into it in great detail but two things would emerge.
First the stakes in terms of political power, foreign and especially in case of Russia domestic, would be extremely raised. In fact the domestic stakes in Russia are already too high to allow Putin to risk losing this war.
Second the possibility of Russia losing would immediately increase as that would be the exact point of delivering weapons from a military perspective.

As such Russia would commit a larger number of their forces to winning this war. However other than Ukrainian personal given western weapons Russian troops are better trained, organized and used to their weapons. Delivering only weapons into the Ukraine thus will not increase its footing in this war. On the downside a plus on weapons on both sides would increase the overall military activities and therefore cause larger amounts of destruction then we would see without.

Should Nato decide to intervene directly with its own troops Russia feel forced to totally commit to this war at which point the Ukraine as a whole would be destroyed independently of who wins.

Tl;Dr: Increased direct or indirect military activity from the west would only increase the amount of destruction in the Ukraine without changing the situation unless one is willed to cause the total destruction of the Ukraine in order to win this war.

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