When the Spanish-American War took place in 1898, Spain had a number of strengths and weaknesses compared to the United States.

Strengths

In the far-flung colonies in which the war was fought, the Spanish already had a military presence. They did not need to take the time to raise, mobilize, and transport their fighting forces since they were mostly already in place. Furthermore, the Spanish military forces in Cuba and the Philippines were more battle-tested since they had been fighting insurrections there for some time. This also meant that they were familiar with the terrain and had military fortifications in place.

Weaknesses

The Spanish navy was severely outdated compared to that of the US Navy. Most of their ships were decades old, whereas the United States had a more modern fleet. Even though both sides had not fought a significant naval battle in recent years, the US Navy had been actively drilling and practicing maneuvers for some time and was therefore better prepared.

The Spanish did not have the support of the local populations. The Cubans and Filipinos were much more eager to aid the Americans, who they viewed as liberators, than the Spanish.

Morale was also an issue for the Spanish. Many Spanish military leaders, as well as rank and file soldiers/sailors, viewed their fight against the United States as doomed from the start. They were tired of years of fighting insurgents in their overseas territories and had little appetite to take on a strong military power like the United States. The Americans, on the other hand, went to war with an extreme sense of optimism.

The war was fought in 1898 and lasted ten weeks. The conflict was fought in both the Caribbean and the Pacific. The main issue in the conflict was Cuban independence. The war was won by the United States and was followed by the Treaty of Paris, which was signed on 10 December 1898. Spain relinquished all of the remaining Spanish Empire, particularly Cuba. Puerto Rico, Guam, and the Philippines were ceded to the United States.

The enemy in this regard, Spain, encountered both advantages and disadvantages during the conflict:

Advantages:

• Spanish garrisons were spread across the areas involved in the conflict.
• The Spanish had naval bases in the territories it occupied, which could benefit it during engagement or protect against sudden attacks.
• In some battles, the Spanish scored victories using ambush tactics, such as in the Battle of Las Guasimas on June 24.
• Spanish troops were equipped with smokeless powder weapons, which helped in hiding their positions while firing.
• The Americans troops suffered many casualties from mosquito-borne disease and heat exhaustion.

Disadvantages:

• The Americans had better equipped naval forces and soon destroyed the Spanish naval fleet.
• Many Cubans were fighting for freedom and the Spanish had to contend with their rebellion. Many Cubans fought against them.
• The American forces were assisted in Cuba by the pro-independence rebels led by General Calixto Garcia.
• In some battles, the Americans used rapid fire Gatling guns that ensured victory, as at the Battles of San Juan Hill and El Caney.
• The new Spanish Government was in disarray.
• Guam was easily captured since they did not even know that their mother country was at war.
• The Americans had many men who volunteered for service in Cuba since they had been encouraged by their own battles during the civil war and believed that Cubans needed their support to gain independence.
• Many African American men volunteered since they believed that fighting for their country would give them credibility. These two actions boosted the number of troops.

It should also be said that the Spanish Empire was at its end, and was quite weak compared to the empire of the Conquistadores and the Catholic Church of the 16th and 17th centuries.  They had lost Latin America, the American Southwest, and the riches both mineral and agricultural that accompanied them.  While well-equipped to fight against Cuban and Filipino rebels, and better equipped in the near term than a hastily assembled American army, they had no long term means with which to take on the United States at the end of the 19th century, on land or the oceans.

The Spanish in Cuba had better weapons than most of the American soldiers.  They had rifles that shot cartridges made from smokeless powder.  The Americans used powder that made smoke, which made it completely obvious where they were once they fired a shot.  The Spanish didn't have to reveal themselves when they fired.

The Spanish navy had much older ships that had no chance against the Americans either in Cuba or the Philippines.

What were the strengths and weaknesses of the US Army in the Spanish-American War?

Spanish-American War lasted a little under four months, resulting in a crushing victory for the United States. On the whole, superior naval power helped the Americans to victory, especially in the Pacific theater of conflict. But as regards the US Army, the main strength for the Americans lay with their vastly superior weaponry. American manufacturers were able to produce vast quantities of weapons on an industrial scale—something with which the relatively backward Spanish economy could not compete.

One of the most important weapons used in the conflict was the Gatling gun, which had been produced in the United States for over thirty years prior to the outbreak of the Spanish-American War. Gatling guns proved their worth during the Battle of San Juan Hill in Cuba, one of the bloodiest engagements in the whole conflict. Here, for the first time, they were used offensively rather than defensively. Thanks to their immense firepower, the Americans were able to neutralize the Spanish artillery, which proved decisive in determining the battle's eventual outcome.

Even so, the US Army still had more than its fair share of weaknesses. For one thing, it lacked local knowledge of the terrain on which it was fighting. As the Spanish had been in control of Cuba and the Philippines for some time, they had a head-start on the Americans in terms of local knowledge. That they subsequently failed to exploit this knowledge successfully doesn't change the fact that the Americans were relatively weak in this area.