The Last Centurion, by John Ringo

This book reminds me so much of Heinlein when he was in his prime. Ringo manages to weave some cutting social and political commentary into a great story. This tale doesn't fit into any of Ringo's ongoing sagas, it's a stand-alone, much like Princess of Wands from a few years back.
The action takes place in 2018. The American people have elected a left-leaning female president, Ms. Warrick, in the midst of a war against radical Islam in Iran. The hero of the tale, Bandit Six (we never do learn his real name, just his military code designation), is an Army captain, raised on a large family farm in the Midwest, who gets tasked with a rather "challenging" assignment.
Although the climatologists and the media have been screaming about "global warming" for decades, an astronomer and climate scientist discovers that the Sun is about to go through a period of rapid cooling which will bring temperatures down significantly worldwide over the next decade. To bump this up to the level of a perfect storm, there's an outbreak of the H1N5 bird flu virus in China that turns into a global pandemic in a very short time.
The military is needed at home to help distribute medical supplies and keep order where possible, and so the U.S. immediately begins to pull back most of its troops from all around the world. Though this is a logistical nightmare, it's nothing compared to the effort it would take to bring back all of the vehicles, weapons, ammunition and supplies we've stocked in the conflict zones, so they're all gathered up into huge storage depots and left behind, with a detachment to guard them from the natives. Enter Bandit Six.
He and his men, aided by a detachment of Nepalese, or Nepos, that the British had to leave behind when they pulled out, do their best to defend their mountain of munitions against the various armed factions who keep trying to come take it away, but eventually a force is brought against them that is overwhelming, and they have to blow up the depot and flee the area.
The only place that the Air Force can get a plane into to extract them is an airfield in Turkey, so they have to fight their way across Iraq, link up with Kurdish forces there, and fight their way through Turkey to join up with the faction with whom the State Department  has chosen to work. Ringo has always written some great and reasonably believable military action stories, and this one doesn't disappoint.
Throughout the narration, Bandit Six delivers a soliloquy, a monologue if you will, on so many subjects it's difficult to keep track of them all. He talks about effective industrial farming and ranching techniques and how they compare to organic farming practices. He lectures on solar climate cycles, epidemiology and disaster response, the reality of life under a Caliphate, ancient history of the entire Asia Minor area, societal trust and pioneer barn-raising practices... All of this demonstrates that Ringo is either extremely well-read, or a superb BS'er - maybe a bit of both. As might be expected from a military protagonist's perspective, the slant is pretty conservative, politically speaking.
It's got it all; Sex and War and Rock and Roll. If you're a Ringo fan, or even if you're not, grab a copy!