According to Wikipedia The US spends more on the military than the next 8 countries on the list combined. Several times the budget for the whole European Union. Is somehow President Eisenhower's warning related to the economy or was it the threat it could pose to the Americans' liberty?
In his farewell speech of 1961, Eisenhower warned of growth of the 'military-industrial complex' and the 'potential for the disastrous rise of misplaced power.' It was a speech he began working on two years earlier and went through 21 drafts - which perhaps indicated the importance he placed upon this. Originally the phrase was 'military-industrial-congressional complex' but the word 'congressional' was crossed out and did not make it into the final speech.
The dangers that Eisenhower spoke of are not new, George Washington in 1796 warned of 'overgrown military establishments are under any form of government inauspicious to liberty.'
Times were different back then - there was a Cold War - and Einsenhower would have been worried about the cost of an arms race with the then Soviet Union and given that it at one point it spent a third of its GDP on its military this was a significant worry. The NPR point out that
Before the late 1950s, companies such as Ford built everything from jeeps to bombers but then went back to building cars. But that changed after the Korean War ... it kept a large standing army ... [and began] a technology race with the Soviets.
And this was also echoed by former Secretary of Defense, Robert Gates, who in a speech in 2011 in the Eisenhower library said:
Does the number of warships we have, and are building really put America at risk when the US battle fleet is larger than the next 13 fleets combined - 11 of whom are our allies and partners?
This, then is an argument for cutting military spending. However, going back to Eisenhower's speech, as a warning it appears stronger than this. Perhaps more in line with his warning were the revelations by Edward Snowden on the extent and range of the surveillance by the NSA on its own domestic population. In a sense, everyone was now a suspect. The amount of information that the FBI had on Martin Luther King pales in significance compared to the kind of information that the NSA has on each and every citizen. Laws that were intended to protect citizens from unnecessary, intrusive and illegal surveillance were outpaced by technologies that were pushed through by a political will that believed in 'total information awareness' and 'full-spectrum dominance'. It's probably apposite to note that the NSA did not go to congress to gain sanction for this because more than likely, they knew they had a vanishing chance of getting it.
It's these kinds of abuses of the power invested in the 'military-industrial complex' that Eisenhower was warning of.
Eisenhower's speech isn't strictly about the military-industrial complex, I at least read it as a general warning of how great concentrations of wealth/power in a construct (in this case, he uses the military industrial complex as an example, but it also mentions academia infused with government directed research funds) can lead to that construct having unintended impacts on democracy. At its core, he appears to be pointing out the precarious balancing act that a government has to make, or rather a well functioning one has to make. The balance between security vs liberty, desires vs necessity, short-term gain vs long-term gain, etc etc.
Unless Eisenhower had a follow up explanation for his speech (which I'm unaware of), a definitive 'what did he mean' probably doesn't exist. Outside of reading his speech, and interpreting it.
WWII did make US's war industry stretch to unconceivable limits. A gargantuan deal of funds and effort were also invested to develop nuclear weapon technology in order to end the war sending a clear message to those who dare to fight the US in the future.
However, at the end of the war, such enormous industrial conglomerate just cannot be stopped. OK, some part of it was diverted to other uses, but the specific parts were... specific.
Their power, influence on politics and strategic direction of nationwide events were mostly unrivaled. Some key people tried to change that, but were eventually wiped out of the way.
Korea, Cold War, Vietnam, and most conflicts since then were all forced. The need was synthetically generated and fed to the citizens to ultimately justify the need to use the machina. Many examples can document this. One of the most relevant would be the events -dismissed warnings- preceding 9/11.
This is just the point Eisenhower was warning us about. He was in, knew things, met people. And because he was able to anticipate the problem, he told us about it. But, I'm afraid we did nothing but make the problem bigger, and even more unstoppable.
One of the things Eisenhower warned about was about the development of this war-based economy. Apparently from 1797 to 1941, the United States mainly relied on civilian industries for private support during times of war with the government directly owning their own shipyards and weapons manufacturers. During World War II, there was a shift where private companies starting maintaining and expanding permanent defense divisions to sell defense products to the government. Many technologies like GPS and night-vision goggles went to the civilian market, but it led to many businesses having a focus on making money from selling weapons to combat enemies to the nation. During the Cold War, the defense industry became somewhat tied to the domestic economy, creating a situation where certain companies shutting down their defense departments could affect the regular economy & allows a 'military industrial complex' that needs constant fighting in order to keep these particular departments afloat. This shift, to some degree, is what Eisenhower was warning about.