So I have been studying European History, and my professor, every now and then, has brought up how unprepared Poland was for the first world war. He has painted this sort of picture of what is essentially the Polish riding into battle on horseback with swords and spears against the invading german tanks and armed infantrymen, and subsequently being demolished. How accurate is this image, and if it is accurate then how did Poland get so developmentally behind of the rest of Europe?
Poland as an independent state did not exist at the time of the first world war. Polish independence had been extinguished once in 1795 in the third partition of Poland and then again the Dutchy of Warsaw lost its independence in 1815. At the start of the first world war Poland was split between the German Empire, Russian Empire and Austro-Hungarian Empire. That said there were a number of Polish specific units in the armies of all three nations. The Austrians raised the Polish Legions, the Russians the Puławy Legion and later the Polish Rifle units of various kinds, particularly early in the war the Russians arguably received the most support from their Polish subjects offering the Poles autonomy. But none of these units were particularly unusual in tactics or equipment. There were some Polish cavalry units, particularly prominent might be Galician Uhlans in the Common Army of AH which at times used lances and sabres. However this practice was a fair bit more common on the eastern front due to armies being typically more mobile in general and not as heavily dug in, plus as a very loose rule of thumb proportionally less machineguns. The majority of Poles in all three were still riflemen though.
That a side I think you were probably thinking about the second world war when Poland as an independent country did exist. Here to this is largely a myth born out of Nazi propaganda. The Polish army was behind the Germans during the war, largely because it was a young nation reborn at the end of the first world war, smaller, not as industrialised and poorer than Germany. There was a lack of modern air craft. There were some good Polish armoured vehicle by the standards of 1939, particularly the single turret variant of the 7TP. Most of their tanks were light but that could be said of Germany or the USSR in 1939. A lot were also tankettes which enjoyed a low profile with the variant armed with a 20mm gun that was sufficient to dispatch a PZ I or II if they managed to achieve an ambush. But there weren't enough of them and too many that the Polish did have were machine gun armed tankettes which proved in effective when the Germans could effectively use modern combined arms tactics or bring up infantry anti-tank weapons. There was also a lack of transport vehicles and with the German areal superiority the Polish troops sometimes found themselves being over run or encircled by German forces.
Polish infantry equipment was pretty much par for the course, the Kb wz. 98a, Karabinek wz. 1929 and Karabinek wz. 91/98 series being the standard infantry rifles was a perfectly serviceable bolt action rifles and carbines, not significantly different in quality to the service rifles of most nations of the time, semi-automatic rifles not being used on a large scale by most forces at least until the late war due to production costs. There was a lack of submachine guns in service during the initial invasions and some of the light machine guns and similar weapons could be argued to have been a little dated by 1939 not exceptionally so.
Now the Polish army did use some horsemen. Primarily for the purposes of reconnaissance cavalry and as mounted infantry. Useful to compensate for the lack of transport vehicles, particularly in areas with few or poor roads suitable for wheeled vehicles in bad weather. Lances weren't regularly used at the time of the war and although they were equipped with sabres their primary weapons were still usually bolt action rifles and carbines like everyone else in 1939. They were not unique in his matter. While they used a relatively high proportion of cavalry, around 10% of frontline troops, many of the armies at the time used at least some for recon on messenger purposes.
The idea that Polish Cavalry attempted to charge German armour with lances and sabres is propaganda and never occurred. If Polish cavalry encountered german armour while mounted they would typically fall back in order to dismount and reengage with suitable weapons like anti-tank rifles and guns. The Polish did on rare occasion make cavalry charges against enemy infantry typically those who were under prepared in order to attempt to deal a quick decisive blow against a force out of a prepared position, usually under more desperate conditions.
It sounds like the basic premise of your question is a bit off. Poland didn't exist in WW1 - it was split between Germany, Russia, and Austria-Hungary, and it only came into being at the end of the war. The story you're referring to is from WW2, and it's a mix of propaganda and several different real incidents during the war. The most famous - the Battle of Krojanty - occurred on the first day of the war, and it involved Polish Ulhans charging German reconnaissance elements and driving them from the field before themselves being driven away by the arrival of heavier German units. The story of Polish lancers charging German tanks head-on comes from German propaganda after the campaign.
With that out of the way, the Polish military in 1939 was better prepared than it's often made out to be, but it did suffer from several crucial shortcomings, several of which would prove fatal.
In terms of infantry weapons, the Poles had an array of weapons generally comparable to contemporary armies, but issued in smaller numbers to provide about 60% less firepower:
In development and expected to enter service at the end of 1939 were also the wz.38 20mm cannon and wz.38M semi-automatic rifle, both of which would have offered significant increases in the firepower of Polish infantry.
Cavalry was in use in 1939, but it was hardly a feature exclusive to Poland. The Germans also operated several cavalry units during the invasion of Poland, and even later in the war the Soviets would rely on cavalry with surprising success for several major operations. Getting back to the Polish cavalry, they were intended to serve as highly mobile forces adept at reconnaissance, screening, delaying, and rearguard actions. While they lacked some of the more organic firepower than infantry divisions, Polish cavalry brigades were still equipped with 37mm anti-tank guns for fire support and an armored group with eight armored cars and 13 TKS tankettes. 7 of the 11 brigades would also receive an infantry battalion to improve their organic firepower at the expense of mobility. In 1936, Poland had even developed plans for a modernization of cavalry brigades to consist of:
Unfortunately, the 10th Cavalry Brigade, which was to be the first example of such a unit in Poland, was stymied by the same under-funding that beset the entire Polish rearmament effort, and thus, by 1939, it had just a company of obsolete Vickers Type E tanks and two companies of TKS tankettes, two motorized infantry battlions, a motorized engineer unit, a motorized anti-tank battery, and a 40mm anti-aircraft battery.
For heavier weapons, Poland again was hampered by shortages of funding and materials, so while things like the 37mm anti-tank guns were perfectly adequate, they were available in far fewer numbers than plans called for. Artillery support was largely reliant on leftover WW1 pieces, so Polish gunners often found themselves both outgunned and outnumbered by German guns. A Czech-designed 155mm howitzer was set to enter production at the end of 1939, but it was unavailable when war broke out. Mobility was also an issue, with a shortage of artillery tractors leaving most guns horse-drawn in 1939. Again, not something exclusive to Poland (Germany remained heavily reliant on horse transport for the entire war), but it did impact the ability to provide fire support for more mobile units.
Air defenses tell a similar story. Production of the famed Bofors 40mm gun had been secured, but it was slowed to about half of what was planned by funding issues, and an advanced 75mm gun was struggling to reach service in 1938. Aircraft were surprisingly modern for the mid-30s, notably the Pzl P.11 fighter and Pzl.23 light bomber, but they were outnumbered and poorly organized, being assigned piecemeal to ground units rather than the more centralized organization of the Luftwaffe. The fairly advanced Pzl.37 medium bomber was in service and showed great promise, but Poland had neither the numbers nor organization to put it to effective use.
Operational organization was the biggest shortcoming of the Polish Army and arguably the biggest reason for its rapid collapse. Unlike the Germans, who employed corps headquarters to coordinate divisions and an extensive staff for Armeekorps to coordinate large formations, Polish units were deployed into much less organized operational groups with fewer radios, poorly organized headquarters, and a generally poor understanding of objectives.
The best demonstration of how this impacted the ability to fight would be the Polish defeat at Bzura. There, the Poles launched a major counteroffensive with 8 infantry divisions and around 2-4 cavalry brigades. Attacking the exposed flank of the German 8th Army, they were initially very successful, but the German command and control structure allowed for a quick reaction that the Poles were unable to match. The Germans were able to quickly maneuver in reinforcements to encircle and ultimately destroy nearly the entire Polish force, costing Poland roughly a quarter million soldiers dead, wounded, and captured for fewer than 20,000 German casualties.