These are basic questions that should be asked and answered when teaching American history in elementary school. On April 15, 1861, President Lincoln issued a call for 75,000 troops to "suppress the rebellion." This meant that soldiers would be ordered to Alabama and other states that had already seceded in order to force them back into the Union. It took almost a year for them to arrive in the Tennessee Valley, but this began a military occupation of Alabama that lasted roughly ten years. It's safe to define that period as one of invasion and occupation. You could can it an attack.

http://millercenter.org/academic/americanpresident/keyevents/lincoln

You also asked about interference. I have to assume that you meant interference with travel, commerce and normal social activities. On April 19, 1861, President Lincoln declared a blockade of all Southern ports, directing the U.S. Navy to intercept and stop merchant ships going in and out of Mobile Bay and other Southern harbors. By any definition a blockade is an act of war. Moreover, civilians attempting to travel to and from Alabama were subject to arrest and imprisonment. Under President Lincoln's suspension of the writ of habeas corpus, those imprisoned could be held without trial or even without any specific charges being made.

http://www.nps.gov/fomc/historyculture/the-writ-of-habeus-corpus.htm

President Lincoln believed that people could be arrested for what they might do or say, so anyone thought to be in sympathy with Alabama or the Confederate States could also be subject to arrest and imprisonment.

Any attempt to answer your question about "interference" would not be complete without reference to confiscation and destruction of property in Alabama. Military and civilian agents of the U.S. government were responsible for confiscation and destruction of property in every county in Alabama. Those who attempted to prove their loyalty to the government could plead for reparations, but this wasn't allowed until many years after the war ended, and many claims were rejected.

As a result of these widespread attacks and interferences, most people in Alabama and the Southern states lived in poverty for generations. By 1938 President Roosevelt recognized the extent of these conditions. In that year he appointed a commission to determine what could be done to reverse Federal policies responsible for many of them. Here's a brief letter written by FDR about economic conditions in the South --
http://www.sreb.org/main/Publications/Roosevelt/1938intro.asp