I understand that a large number of important, and very old, buildings were demolished during the wars, but I have also read that both sides (during both conflicts) generally did not target historic landmarks. Is this true, and if so, how/why were such efforts taken during a period of total war?
Although this doesn't cover the entirety of your question, you might be interested in previous threads on WWII aerial bombing and monuments:
Targeting and Historic Sites
What was/was not targeted in bombings during WWII (European theatre)? - 16 comments, over 11 months old.
The commenters here discuss the possible accuracy of the bombings, the priority targets, and the expected effectiveness of the attacks to show how military planners pursued the matter while also dipping into the morality of the situation.
What cultural/historical/etc. artifacts/buildings/documents/etc., if any, were truly lost, i.e. destroyed, in the Second World War? - 15 comments, over 2 years old.
There's a wide variety of examples of Allied bombing damaging or destroying monuments and artifacts in this thread with some discussion over the events and policies that made it happen.
How did famous monuments/buildings survive WWII? - 5 comments, over 1 year old.
European examples are brought up, but there's also some talk about the intentions and effects of high concentration firebombing on Japanese cities and old monuments.
What was the city of Dresden like before WWII? - 19 comments, over 2 years old.
This thread delves into historic sites in Dresden that were destroyed as well as the reasoning and international law surrounding the attack.
Why did Italy remain mostly undamaged in World War 2? - 5 comments, over 2 years old.
The commenters here talk about Italian examples of damaged or destroyed monuments as well as tactics which reduced monument damage during the fighting there to a degree.
Bombing related loss of art and monuments During World War II
Did London loose any iconic/important buildings or other cultural/historical treasures during the Blitz? - 5 comments, over 6 months old.
This talks about the aftereffects of Axis bombings, but not necessarily if it was a deliberate policy to attack or avoid monuments.
How many of the historic buildings of post-WW2 Europe are actually real? - 4 comments, over 7 months old.
The commenters here talk about how damage was distributed throughout various countries and locations within those countries during the war.
The looting and/or non-bombing related destruction of art during World War II
What significant works of art have been destroyed, or nearly destroyed, during war? - 3 comments, over 1 year old.
This thread pulls up some examples from World War II as well as from World War I and 21st century events in Afghanistan.
Do we have images (photographs) of any art that was lost during WWII? - 5 comments, over 9 months old.
There's a variety of answers here, but not much analysis.
What happened to art that was confiscated from Germany by the Soviet Union during the end of World War 2? - 1 comment, over 12 months old.
The lone comment links to two online articles for reading on the matter.
How much art was lost during WW2? - 7 comments, over 9 months old.
There's a variety of links both to what art was lost as well specific actions by various sides that resulted in the theft or destruction of art during the war.
How did Germany deal with entente world war one monuments in occupied France and Belgium? - 12 comments, over 7 months old.
Several examples are brought up, including one particularly in depth analysis of a monument's history and the political ramifications of its destruction.